The Sermon expresses the only righteousness acceptable to God in this or in any age. Jesus offers a closer definition of the constant Divine moral requirement and does not depart from either the creation ethic or that of the Old Testament; consequently, the Sermon is relevant as the standard of conduct, convicting men of sin, restraining public wickedness, and ruling the life of the believer.
Greg Bahnsen. Theonomy in Christian Ethics. CMP: Nacogdoches 2002.