2 Bible Verses about Covenant Obligations

Once again, you have heard how the men of old were told, 'You must not forswear yourself but discharge your vows to the Lord'. But I tell you, you must not swear any oath, neither by heaven, for it is the throne of God, nor by earth, for it is the footstool of his feet, nor by Jerusalem, for it is the city of the great King;read more.
nor shall you swear by your head, for you cannot make a single hair white or black. Let what you say be simply 'yes' or 'no'; whatever exceeds that springs from evil.

To take an illustration from human life, my brothers. Once a man's will is ratified, no one else annuls it or adds a codicil to it.