
What, then, is the essential characteristic of the true believer, the genuine disciple of Jesus Christ? It is not loud profession, nor spectacular spiritual triumphs, nor protestations of great spiritual experience. Rather, his chief characteristic is obedience. True believers perform the will of their Father, consistent with their prayer, “Your will be done on earth as in heaven.” They cannot forget that at the beginning of the Sermon on the Mount, Jesus said, “Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven. For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven” (5:19f.). And so they practice obedience. The Father’s will is not simply admired, discussed, praised, debated; it is done. It is not theologically analyzed, nor congratulated for its high ethical tones; it is done. The test is rephrased by a famous second-century document, the Didache, which says, “But not everyone who speaks in the Spirit is a prophet, except he have the behavior of the Lord.”
D.A. Carson, Jesus’ Sermon on the Mount and His Confrontation with the World: An Exposition of Matthew 5-10, p. 138