A few inconclusive suggestions about the strange story at the end of Matthew 17.
First, I take the majority view that the tax in question is the temple tax, and that helps to explain the distinction of sons and strangers that Jesus makes. In a temple context, the sons are those who are members of the house, who have access to the king, in short, priests. Strangers are the “unauthorized” who are not permitted in the house. When Jesus includes Himself and Peter under the rubric of “sons,” He is claiming access to the Father, hinting at the coming of a new temple with a reorganized priesthood.
Second, Jesus is willing to give money to the temple to support the temple’s operation. He is not obligated, but He gives the tax anyway. Thus, he stakes a position on what appears to be a debate among Jews of the first century concerning the legitimacy of the temple leadership and the legitimacy of the tax. His reasoning indicates that He is free to pay or not, but He ends up affirming Peter’s initial answer – Yes, the teacher does pay the tax.
Third, what’s this business with fishing? On one level, it supports Jesus’ conclusion about giving the tax even though He’s exempt. How can disciples of Jesus willingly give up their freedoms, pay money they don’t owe? Won’t that bankrupt them? This is the same question that arises from Jesus’ teaching in the Sermon on the Mount: If we have to give up our cloak, won’t we end up naked? Jesus demonstrates to Peter that he has nothing to fear from going along with unnecessary and even oppressive taxation. Peter can be defrauded, and still have all he needs because the Father can make fish cough up coins.
Finally, if the tax is the temple tax, used to support the operations of the temple, then the coin that comes from the mouth of the fish is money from the sea going to support the worship of the temple. The sea and the fish of the sea are common images of Gentiles, and this fishing expedition links to various prophecies about the Gentiles bringing their treasures to the temple. Peter is a fisher of men, and the men he reels in will give up their treasures to Jesus’ temple.