PuritanBoard Honor Roll
How so? Of course neither fellowship nor speech are in and of themselves sinful activities in which to engage on the Lord's Day. But the key issue is what type of fellowship and speech goes on, what what is done and discussed during that time. If one is to draw any consistent line whatsoever anywhere in-between something like a football game and, say, a discussion on life, marriage or the Word over dinner with one's children, one must define certain types of fellowship and discussion as biblical on the Lord's Day, and other types as unbiblical.
I would not even call any and all birthday celebrations necessarily sinful in and of themselves on the Lord's Day. It could possibly done in the total context of a loose family worship type of setting, with a decided focus toward thanking God for His gifts of life, family, children, parents and fellowship. But as Christopher noted well above, a typical birthday party held by an unbeliever will be a far cry from that, and in many ways the type of discussion and activity present would most likely be non-differentiable in principle from that at a sports game.
Furthermore, of course Matthew himself could try to individually make his own contributions to the fellowship and discussion consist of a healthy, God-centered focus on life and family, but the vast majority of most people's focus and the discussion which would continually abide would not be God-centered in that way, and as such he would most likely be surrounded by unbiblical practice and discussion on the Lord's Day. It would likely be somewhat similar (again, non-differentiable in principle) to going to an unbelieving nephew's college football game on the Lord's Day, hoping oneself to only discuss and focus on God-centered things with the rest of the people, despite what they came there to do. In such a case, do you think such things would really become the sole focus of the outing? Hardly.
Apples and oranges? Not really.
I think this articulates the most or all of the issues that must be considered.