Praised be Jesus and Mary, now and forever.
In today's Gospel, Jesus' enemies ask him a question to ensnare him. Some background will help us to understand the trap. God had given authority to the house of David, but no king of his line had ruled for centuries. About a hundred years before Christ, the Romans had been called in to intervene in a civil war. They restored peace, but they made Judah a Roman province. Many Jews resented being under the dominion of pagans who went so far as to dictate who could and could not be the high priest. Some said that it was wrong to support the Roman government by paying taxes. Already, back when Jesus was a child, around the time he was going to the temple, around the time that he was lost in Jerusalem, A.D. 6 or 7, when the Romans decided to take a census and collect taxes, a man named Judas stirred up a rebellion in Galilee. He was killed and all his followers were scattered.
This seems to have been the origin of the zealot party. The zealots continued to cause trouble for the Romans even after the time of Jesus. So the question about paying the tax was a way of getting Jesus to declare whether or not the Roman domination of the Holy Land was legitimate. And this is why there are those two groups there, the Pharisees and the Herodians. If he spoke against that, the Herodians were there to denounce him to the authorities as a rebel. If he spoke for it, the Pharisees were ready to denounce him to the people as a friend of the tax collectors. The Herodians and the Pharisees had little in common except opposition to Jesus. The Herodians were a political group, the clients and the partisans of Herod Antipas, the tetrarch of Galilee, whose power had been confirmed by Rome. The Pharisees were zealous for exacting observance of the Torah, though they tended to get lost in the details of it. When these two ask Jesus their question to ensnare him, he immediately recognizes their hypocrisy. Their question does not deserve an answer because they are not seeking the truth. However, he will nevertheless teach them something important. He doesn't say anything about whether or not the Roman occupation was legitimate. By asking his question for a coin, he shows that they are benefiting from the peace and economic system established by the Romans. And therefore, they have the duty to pay taxes to support that system. The image and inscription prove that the money is Caesar's. So if you accept Caesar's money, you must accept his taxes, but give to God what is God's.
So we've seen in this passage a justification for the modern idea of separation of church and state, in the sense that there are some matters which are the purview of the church, others which belong to the state, and a complete separation between the two. This view, apart from other problems, is anachronistic. No one in first-century Palestine had a secular idea of the state. Everyone believed that religion was important for national success. They just differed on what God or gods ought to be worshipped. The temporal realities do have a legitimate authority, but it is never an absolute or a legitimate autonomy, but that autonomy is never absolute. 
Repay to Caesar what belongs to Caesar, Jesus says. The coin is Caesar's, for it bears his image and inscription. But give to God what belongs to God. And so what is it that bears the image and inscription of God? God created man in his image, and sin can only obscure that image, not destroy it. Saint Augustine sees the image of God particularly in the soul, whose powers reflect the Trinity. What about God's inscription? In Jeremiah we read, this is the covenant I will make with the house of Israel after those days, declares the Lord. I will put my law within them, and I will write it on their hearts. His law is inscribed upon our hearts. The government does have the right to impose taxes within the limits of justice, but it does not have the right to impose sins. And so the Catechism of the Catholic Church says, the citizen is obliged in conscience not to follow the directives of civil authorities when they are contrary to the demands of the moral order, to the fundamental rights of persons or the teachings of the gospel. Civil authority regards this world which is passing away. Divine authority calls us to prepare for eternity.
Today's reading from the second letter of Saint Peter reminds us that the present world will be dissolved or melted by fire. We should not be terrified by this, but rather hasten its coming. When Christ comes at the end of the world as the judge of the living and the dead, he wants to judge as many as possible worthy of heaven. So I would say we hasten his coming by making ourselves and as many others as possible worthy of heaven. After the elements are melted by fire, we await new heavens and a new earth in which righteousness dwells. This is why we should want to hasten its coming, in order to receive the good things that are to come. There will be no room in that new universe for anyone or anything that is evil, and so we must be eager to be found without spot or blemish before him. As Saint Paul puts it, we must become holy and immaculate. The church must become like Mary, the type or model of the church, through her mediation.
It may sound from what Saint Peter says that the current heavens and earth will be destroyed, but the Fathers teach rather that they will be transformed. For, says Saint Peter, he did not say other heavens and another earth, but the old and ancient one to be changed for the better. He goes on to quote Psalm 102 to demonstrate this. In the beginning, Lord, you founded the earth, and the heavens are the works of your hands. They will perish, but you will remain, and they will all grow old as a garment, and you will change them as a piece of clothing, and they shall be changed. He concludes, as for the things, therefore, that will perish, grow old, and be changed, it is definitely clear that once they have been consumed by the fire, they resume a more pleasing appearance as soon as the fire goes out. I think this is also shown by what Saint Paul writes to the Romans. He says, the creation was subjected to futility, not willingly, but because of him who subjected it, in hope that the creation itself will be set free from its bondage to corruption and obtain the freedom of the glory of the children of God. If the heavens and the earth were to be destroyed rather than transformed, they would not inherit that freedom. They would not obtain that freedom. 
This is also similar to what will happen to our bodies in the eternal resurrection. When we die, even the bodies of the just are usually ruined by death and decay, but at the end of the world, they will rise in glory. Not new bodies, but the same bodies transformed and made glorious, made a worthy dwelling for the righteous. 
While we await the renewal of the universe and of our own bodies, we must cooperate with God's grace to make ourselves worthy to enjoy these new things. If they do not come immediately, consider the patience of our Lord as salvation, Saint Peter says. He's concisely repeating what he said a little before today's reading. The Lord is not slow to fulfill his promise, as some count slowness, but is patient toward you, not wishing that any should perish, but that all should reach repentance. So if the end of the world does not come quickly, it is because God is giving time to repent. It is slow in coming because people are slow to make themselves ready for heaven rather than hell.
The reading then skips over what Saint Peter said about Saint Paul. Realizing that he's teaching the same things, he mentions the fact that Saint Paul also teaches them. But he adds, Saint Peter adds, there are some things in his letters that are hard to understand, which the ignorant and unstable twist to their own destruction as they do the other scriptures. He goes on to say the words that we heard, since you are forewarned, be on your guard not to be led into the error of the unprincipled and to fall from your own stability. You are forewarned that there are people who misunderstand Saint Paul, and so teach heresies, claiming that they're what the Bible says. Do not let them lead you astray, but remain stable, that is, steadfast in the faith you have received. Give to God what is God's. Give him yourself.
Praised be Jesus and Mary, now and forever.