13 “I will pay my vows unto the Lord”. What vows will you pay? What victims have you vowed? What burnt-offerings, what holocausts? Do you refer to what you have said a little before, “I will receive the cup of salvation, and will call upon the Name of the Lord;” and, “I will offer to You the sacrifice of thanksgiving”? And indeed whosoever well considers what he is vowing to the Lord, and what vows he is paying, let him vow himself, let him pay himself as a vow: this is exacted, this is due. On looking at the coin, the Lord says, “Render unto Cæsar the things which are Cæsar's, and unto God the things which are God's:” his own image is rendered unto Cæsar: let His image be rendered unto God.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)