On the face of it, this is about paying taxes. Jesus seems to say we should pay taxes. And he has good reason for this. To encourage the people not to pay taxes would be to subject them to punishment from Rome, which could mean death. As we know, Jesus did not come to incite a violent uprising or encourage people to be killed.
However, the question about paying taxes was not just a political question. It was also a moral and theological question. What is legal is not necessarily moral. What is lawful from Rome’s perspective might not be acceptable to God.
Paying to God what is God’s, is about us participating in God’s kingdom – and this in itself was entirely subversive in Roman times where Caesar was considered a type of God.