“Then the sons are exempt,” Jesus said to him. “But so that we may not offend them, go to the lake and throw out your line. Take the first fish you catch; open its mouth and you will find a four-drachma coin. Take it and give it to them for my tax and yours.”
To explain many points, the students of Jesus were told to go and collect money for paying tax from from the mouth of a fish. The Master explained to His students that they did not have to pay tax, but that they should pay anyhow. Simply because people of this World could put them into trouble as claimed to be «tax defaulters». Since Jesus came from Heaven, and gave us a citizenship in Heaven, all we have belongs to our Father in Heaven.