Today's Gospel is Jesus' famous cut-to-the-chase response to a question meant to trip him up. (Note: it is not a good idea to try to catch God in a slip of the tongue.)
What "belongs" to Caesar? The letter to the Romans (and the first letter of Peter) tell us that we owe "respect" (and taxes, too). But what about God, then? According to Peter and Paul, that would not be "respect," but "fear" (or "reverence" if you will). But I like to connect this to another Gospel passage, where Jesus is more detailed about "what belongs to God": "all your heart, all your mind, and all your strength."