Jesus is saying that those who willingly use the coin that is Casesar's should repay him in kind. And they should repay God with the good deeds that are his due.
While here on earth, we must follow the laws of our government, which includes paying taxes for the money we spend or incur. We must also be preparing for our eternity in heaven, and "repay" for that with good deeds we give up to God. Think of it this way: if you live on w piece of property, you pay property tax to the government as they allow to live there. We won't have to pay to be in heaven. Because of Jesus, we don't have to pay to get there. But just being a good Christian and going to church is not doing our share. We need to be spreading the good word of God, and we can do this with our good deeds. This is a way to "repay" or merely thank God for giving us Jesus and allowing us the chance to spend eternity with him.
Dear Lord, help me to see ways daily to repay you with good deeds. Amen.