Jesus and Oaths
Matthew 5:34-37 " But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God, 35 or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King.36 And do not take an oath by your head, for you cannot make one hair white or black. 37 Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil."
Man's is corrupt, but God's Law is not corrupt. Jesus is saying that God is the only one who has the authority to say these ultimate things, so when God makes a promise it is never broken.