2 Bible Verses about Covenant Obligations

Again ye have heard that it was said to those of old, "Thou shalt not perjure thyself, but shalt perform to the Lord thine oaths:" But I say to thee, Swear not at all; neither by the heaven; for it is the throne of God: nor by the earth; for it is the footstool of his feet: nor by Jerusalem; for it is the city of the great King:read more.
neither shalt thou swear by thy head, for thou canst not make one hair white or black. But let your discourse be, Yea, yea; No, no: for all addition to these is from the wicked one.

Brethren, I speak humanly; to use a similitude, a man's testament, if it be passed in legal form, no man can vacate, or add thereunto.