From: Matthew 17:22-27
Second Prophecy of the Passion; the Temple Tax
 As they were gathering in Galilee, Jesus said to them, "The Son of Man is to be delivered into the hands of men,  and they will kill Him, and He will be raised on the third day." And they were greatly distressed.
 When they came to Capernaum, the collectors of the half-shekel tax went up to Peter and said, "Does not your Teacher pay the tax?" 25] He said, "Yes." And when he came home, Jesus spoke to him first, saying, "What do you think, Simon? From whom do kings of the earth take toll or tribute? From their sons or from others?"  And when he said, "From others," Jesus said to him, "Then the sons are free.  However, not to give offense to them, go to the sea and cast a hook, and take the first fish that comes up, and when you open its mouth you will find a shekel; take that and give to them for Me and for yourself."
24-27. "Half-shekel", or "didrachma": a coin equal in value to the annual contribution every Jew had to make for the upkeep of the temple--a day's wage of a laborer. The shekel or stater which our Lord refers to in verse 27 was a Greek coin worth two didrachmas.
Jesus uses things great and small to get His teaching across to His disciples. Peter, who is to be the rock on which He will found His Church (Matthew 16:18-19), He prepares by letting him see His dramatic Transfiguration (17:1-8); now He gives Peter another inkling of His divinity through an apparently unimportant miracle. We should take note of Jesus' teaching method: after His second announcement of His passion, His disciples are downhearted (Matthew 17:22-23); here He lifts Peter's spirits with this friendly little miracle.
26. This shows how conscientiously our Lord fulfilled His civic duties. Although the half-shekel tax had to do with religion, given the theocratic structure of Israel at the time, payment of this tax also constituted a civic obligation.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.