2 Bible Verses about Covenant Obligations

Again, ye have heard that it hath been said to the antients, "Thou shalt not for swear thy self, but shalt perform unto the Lord thine oaths." but I say unto you, swear not at all; neither by heaven, for it is God's throne: nor by the earth, for it is his footstool: nor by Jerusalem, for it is the city of the great King.read more.
neither shalt thou swear by thy head, because thou canst not make one hair white or black. but let your communication be, yes, yes; no, no: for whatever goes beyond this, is evil.

Brethren, I speak according to the practice of men; contracts between men, when once ratified, cannot be disannulled or altered afterwards by any man.