Some summary and gleanings over many years looking at this question regarding Calvin and observance of the old pretended holy days. Most of this comes from everything I've learned of Calvin on the subject covered in "In Translatiōne: John Calvin’s Letters to the Ministers of Montbéliard (1543–1544): The Genevan Reformer’s Advice and Views of the Liturgical Calendar," The Confessional Presbyterian 13 (2017): 198-220.
Calvin tolerated the old holy days of necessity but worked and advised against observing them. If one could win out from under them, one should never go back to them; he'd think many in our day mad. I'd say he was pretty consistent in opposing the old pretended holy days. He didn't think one should be over-scrupulous about them; but he was willing to put his ministry at stake when such things were imposed. He agreed with their removal under Farel's reforms in Geneva, retaining only the Lord's Day, and got banished with Farel among other reasons for disagreement with the imposition of Bern's five retained holy days upon Geneva. His advice remained consistent also. "I would wish that you were more steadfast in not submitting to feast days. But I think that you should do so in such a way that you are not arguing about every conceivable point, but only about those matters which do not serve to edify, and very obviously reek of superstition. And you already have a reasonable grounds for refusal. For in the papacy they worshiped the conception and ascension of the Virgin with great frequency. What will the servant of Christ have to say if he should climb into the pulpit on those days, except that he holds in contempt the foolishness of those people who have dreamed up these holy days?" Calvin, Letter to the ministers of Montbéliard (October 7, 1543), in The Confessional Presbyterian 13 (2017), 217. "With respect to ceremonies and above all the observance of holy days [I offer the following]: Although there are some who eagerly long to remain in conformity with such practices, I do not know how they can do so without disregard for the edification of the church, nor [do I know] how they can render an account to God for having advanced evil and impeded its solution…. Nevertheless, since we have to endure a number of imperfections when we cannot correct them, I am of the opinion that no brother ought to allow the above to be the cause of his leaving his church, unless the majority support the opposite." Letter, December 25, 1557, in Calvin’s Ecclesiastical Advice, p. 90.
In the 1540s, after his return to Geneva, Calvin had as part of the agreement conceded to abide by the Bernese imposed feast days, but, he immediately and steadily worked to get rid of them! By 1550, the small council had had enough and outlawed the remaining days and made Christmas into simply a sermon preached on Christ’s birth on the closest Lord’s day. About this time, Calvin was surprised by a larger audience than usual on a weekday that fell on December 25, 1550/51.
"Now, I see here today more people that I am accustomed to having at the sermon. Why is that? It is Christmas day. And who told you this? You poor beasts. That is a fitting euphemism for all of you who have come here today to honor Noel. Did you think you would be honoring God? Consider what sort of obedience to God your coming displays. In your mind, you are celebrating a holiday for God, or turning today into one but so much for that. In truth, as you have often been admonished, it is good to set aside one day out of the year in which we are reminded of all the good that has occurred because of Christ’s birth in the world, and in which we hear the story of his birth retold, which will be done Sunday. But if you think that Jesus Christ was born today, you are as crazed as wild beasts. For when you elevate one day alone for the purpose of worshipping God, you have just turned it into an idol. True, you insist that you have done so for the honor of God, but it is more for the honor of the devil.
Let us consider what our Lord has to say on the matter. Was it not Saul’s intention to worship God when he spared Agag, the king of the Amalekites, along with the best spoils and cattle? He says as much: ‘I want to worship God.’ Saul’s tongue was full of devotion and good intention. But what was the response he received? ‘You soothsayer! You heretic! You apostate! You claim to be honoring God, but God rejects you and disavows all that you have done.’ Consequently, the same is true of our actions. For no day is superior to another. It matters not whether we recall our Lord’s nativity on a Wednesday, Thursday, or some other day. But when we insist on establishing a service of worship based on our whim, we blaspheme God, and create an idol, though we have done it all in the name of God.73 And when you worship God in the idleness of a holiday spirit, that is a heavy sin to bear, and one which attracts others about it, until we reach the height of iniquity. Therefore, let us pay attention to what Micah is saying here, that God must not only strip away things that are bad in themselves, but must also eliminate anything that might foster superstition. Once we have understood that, we will no longer find it strange that Noel is not being observed today, but that on Sunday we will celebrate the Lord’s Supper and recite the story of the nativity of our Lord Jesus Christ. But all those who barely know Jesus Christ, or that we must be subject to him, and that God removes all those impediments that prevent us from coming to him, these folk, I say, will at best grit their teeth. They came here in anticipation of celebrating a wrong intention, but will leave with it wholly unfulfilled.74
73. “In the creation of a festival, an idol, the product of human fantasy, was forged in the name of God.” Leith, p. 214.
74. Farley, Sermons on the Book of Micah, pp. 302–304."
Cited from, "In Translatiōne: John Calvin’s Letters to the Ministers of Montbéliard (1543–1544): The Genevan Reformer’s Advice and Views of the Liturgical Calendar," The Confessional Presbyterian 13 (2017): 209-210.
Calvin also preached ‘on’ Epiphany (January 6, 1551, just days after his famous and often referenced sermon from the same Book of Micah on December 25, 1550/51—the first of the year at that time).
“If we would worship God as we should, then this passage [Micah 6:12-16] forces us to expend the effort to ground ourselves in the pure simplicity that God has set forth in his Word.
“That constitutes a doctrine we cannot ignore….
“Now by this example, we are instructed to adhere to the pure simplicity of God’s Word, even though we are prone to disregard it…. For although one might daily explain what has been done in order to worship God, the majority will continue to pursue their habitual course and old superstitions. For example, how many people still regard Epiphany with high reverence? They even celebrate the festival as they have been accustomed to do. I know not where they came up with this festival of 'the king.'
“Now even though people openly know that all this is pure mockery of God … if you were to ask three hundred, or even a thousand Genevan inhabitants, if it were good to celebrate this festival, they would reply: 'Why not? What harm can result from honoring God in this way?' That is the response that many would make, even though they are supposed to be instructed in the Word of God and know that such falsehood is nonsense. This is not how we should act. For if we hope to worship God in the manner that is acceptable to Him, we must divest ourselves of all silly superstitions and frivolous inventions, renounce all idolatry in order to worship God in spirit and in truth (as God commands us), and cling to the simplicity that we observe in his Word.”
Calvin, Sermons on the Book of Micah, trans. Farley, pp. 362–364.
Calvin tolerated the old holy days of necessity but worked and advised against observing them. If one could win out from under them, one should never go back to them; he'd think many in our day mad. I'd say he was pretty consistent in opposing the old pretended holy days. He didn't think one should be over-scrupulous about them; but he was willing to put his ministry at stake when such things were imposed. He agreed with their removal under Farel's reforms in Geneva, retaining only the Lord's Day, and got banished with Farel among other reasons for disagreement with the imposition of Bern's five retained holy days upon Geneva. His advice remained consistent also. "I would wish that you were more steadfast in not submitting to feast days. But I think that you should do so in such a way that you are not arguing about every conceivable point, but only about those matters which do not serve to edify, and very obviously reek of superstition. And you already have a reasonable grounds for refusal. For in the papacy they worshiped the conception and ascension of the Virgin with great frequency. What will the servant of Christ have to say if he should climb into the pulpit on those days, except that he holds in contempt the foolishness of those people who have dreamed up these holy days?" Calvin, Letter to the ministers of Montbéliard (October 7, 1543), in The Confessional Presbyterian 13 (2017), 217. "With respect to ceremonies and above all the observance of holy days [I offer the following]: Although there are some who eagerly long to remain in conformity with such practices, I do not know how they can do so without disregard for the edification of the church, nor [do I know] how they can render an account to God for having advanced evil and impeded its solution…. Nevertheless, since we have to endure a number of imperfections when we cannot correct them, I am of the opinion that no brother ought to allow the above to be the cause of his leaving his church, unless the majority support the opposite." Letter, December 25, 1557, in Calvin’s Ecclesiastical Advice, p. 90.
In the 1540s, after his return to Geneva, Calvin had as part of the agreement conceded to abide by the Bernese imposed feast days, but, he immediately and steadily worked to get rid of them! By 1550, the small council had had enough and outlawed the remaining days and made Christmas into simply a sermon preached on Christ’s birth on the closest Lord’s day. About this time, Calvin was surprised by a larger audience than usual on a weekday that fell on December 25, 1550/51.
"Now, I see here today more people that I am accustomed to having at the sermon. Why is that? It is Christmas day. And who told you this? You poor beasts. That is a fitting euphemism for all of you who have come here today to honor Noel. Did you think you would be honoring God? Consider what sort of obedience to God your coming displays. In your mind, you are celebrating a holiday for God, or turning today into one but so much for that. In truth, as you have often been admonished, it is good to set aside one day out of the year in which we are reminded of all the good that has occurred because of Christ’s birth in the world, and in which we hear the story of his birth retold, which will be done Sunday. But if you think that Jesus Christ was born today, you are as crazed as wild beasts. For when you elevate one day alone for the purpose of worshipping God, you have just turned it into an idol. True, you insist that you have done so for the honor of God, but it is more for the honor of the devil.
Let us consider what our Lord has to say on the matter. Was it not Saul’s intention to worship God when he spared Agag, the king of the Amalekites, along with the best spoils and cattle? He says as much: ‘I want to worship God.’ Saul’s tongue was full of devotion and good intention. But what was the response he received? ‘You soothsayer! You heretic! You apostate! You claim to be honoring God, but God rejects you and disavows all that you have done.’ Consequently, the same is true of our actions. For no day is superior to another. It matters not whether we recall our Lord’s nativity on a Wednesday, Thursday, or some other day. But when we insist on establishing a service of worship based on our whim, we blaspheme God, and create an idol, though we have done it all in the name of God.73 And when you worship God in the idleness of a holiday spirit, that is a heavy sin to bear, and one which attracts others about it, until we reach the height of iniquity. Therefore, let us pay attention to what Micah is saying here, that God must not only strip away things that are bad in themselves, but must also eliminate anything that might foster superstition. Once we have understood that, we will no longer find it strange that Noel is not being observed today, but that on Sunday we will celebrate the Lord’s Supper and recite the story of the nativity of our Lord Jesus Christ. But all those who barely know Jesus Christ, or that we must be subject to him, and that God removes all those impediments that prevent us from coming to him, these folk, I say, will at best grit their teeth. They came here in anticipation of celebrating a wrong intention, but will leave with it wholly unfulfilled.74
73. “In the creation of a festival, an idol, the product of human fantasy, was forged in the name of God.” Leith, p. 214.
74. Farley, Sermons on the Book of Micah, pp. 302–304."
Cited from, "In Translatiōne: John Calvin’s Letters to the Ministers of Montbéliard (1543–1544): The Genevan Reformer’s Advice and Views of the Liturgical Calendar," The Confessional Presbyterian 13 (2017): 209-210.
Calvin also preached ‘on’ Epiphany (January 6, 1551, just days after his famous and often referenced sermon from the same Book of Micah on December 25, 1550/51—the first of the year at that time).
“If we would worship God as we should, then this passage [Micah 6:12-16] forces us to expend the effort to ground ourselves in the pure simplicity that God has set forth in his Word.
“That constitutes a doctrine we cannot ignore….
“Now by this example, we are instructed to adhere to the pure simplicity of God’s Word, even though we are prone to disregard it…. For although one might daily explain what has been done in order to worship God, the majority will continue to pursue their habitual course and old superstitions. For example, how many people still regard Epiphany with high reverence? They even celebrate the festival as they have been accustomed to do. I know not where they came up with this festival of 'the king.'
“Now even though people openly know that all this is pure mockery of God … if you were to ask three hundred, or even a thousand Genevan inhabitants, if it were good to celebrate this festival, they would reply: 'Why not? What harm can result from honoring God in this way?' That is the response that many would make, even though they are supposed to be instructed in the Word of God and know that such falsehood is nonsense. This is not how we should act. For if we hope to worship God in the manner that is acceptable to Him, we must divest ourselves of all silly superstitions and frivolous inventions, renounce all idolatry in order to worship God in spirit and in truth (as God commands us), and cling to the simplicity that we observe in his Word.”
Calvin, Sermons on the Book of Micah, trans. Farley, pp. 362–364.
