Spiritual spying, from William Perkins (Galatians, 1617, 74, 75):
There be two kinds of spying: one lawful, the other unlawful. Lawful, as when in just and lawful war we inquire into the counsels and doings of our enemies, Numb. 13:1. Unlawful, when men pry into any thing or matter to find a fault. Thus hypocrites spy faults in the persons and lives of men, that they may have somewhat whereby to disgrace them, Matt. 7:4. Thus atheists pry into the scriptures that they may confute them. Thus sundry hearers come to sermons that they may carp. Thus our enemies inquire into our religion that they may find (as they suppose) exceptions, untruths, and contradictions. And in the church of Jerusalem, false brethren inquire how far Christian liberty extends that they may overthrow it. This kind of spying is a common fault; we must take heed of it, and apply the eye of our mind to a better use. First, we are to be spies in respect of our own sins and corruptions, to spy them out; Lam. 3:40, let us search our ways, and inquire, and turn again to the Lord. Again, we are to play the spies in respect of our spiritual enemies, that we may find out the temptations of the flesh, the world, and the devil. Thirdly, we must be as spies in searching of the Scriptures, John 5:39, that we may understand the words of the law of God, and find comfort to our souls.