In today's Gospel reading from Mark 12, Jesus said to the Pharisees and Herodians out to test him, “Repay to Caesar what belongs to Caesar and to God what belongs to God.” Having failed to ensnared him, they were amazed at his reply.
What exactly of us belongs to God? It's clear that the whole of us belongs to him. Why not start with the heart, the most important part to us? When you are at it, throw in your mind as well. Offer your heart and mind to God and he will purify both, filling the heart with his love and enlightening the mind with his wisdom. And we become a new creature, pleasing to ourselves and delightful to him. A great way to pay what's due.