2 Bible Verses about Covenant Obligations

Again ye have heard that it was said to them of old time, "Thou shalt not swear falsely, but shalt perform to the Lord thine oaths." But I say to you, Swear not at all; neither by heaven, for it is the throne of God; nor by the earth, for it is his footstool; nor by Jerusalem, for it is the city of the Great King;read more.
nor shalt thou swear by thy head, for thou canst not make one hair white or black. But let your language be, Yea, yea; Nay; nay; for whatever is more than these cometh of evil.

Brethren, I speak according to what is practised among men; no one sets aside even a human covenant, or makes additions to it, after it has been ratified.