The chapter
Simply Three of them see him changed on a mountain with Moses and Elijah. Coming down, a father asks for a son the disciples could not help. Then a second warning about what is coming, and a question about a temple tax.
Context The voice on the mountain says what the voice at the baptism said, word for word, and adds three words: listen to him. Matthew has given the same sentence twice, at the start of the ministry and at its turn.
Verses 1-13
Simply His face shines and his clothes go white, Moses and Elijah appear, and Peter offers to build three shelters. A cloud covers them and a voice speaks. Coming down, they ask about Elijah, and he says Elijah has already come.
Context Verse 13 is Matthew closing a thread he opened in chapter 3 and named in chapter 11: the disciples understand he was speaking of John. He also says that they did to Elijah whatever they wanted, which the reader has already been shown at 14:10.
Verses 14-23
Simply A father kneels for a son who falls into fire and water. The disciples could not cure him. He does, and tells them the reason was their unbelief: faith the size of a mustard seed would move a mountain.
Context The measure he gives is deliberately the smallest thing in the chapter and the smallest thing he has used before, the mustard seed of chapter 13. The second announcement of what is coming ends with the disciples being exceedingly sorry, which is Matthew reporting the effect rather than the argument.
Verses 24-27
Simply Collectors ask Peter whether his teacher pays the temple tax. Jesus asks whether kings take tribute from their own children or from strangers, concludes that the children are exempt, and pays it anyway.
Context The reason given for paying is not the argument he has just made but the opposite of it: so as not to cause them to stumble. It is the only place in the Gospel where he wins a point and then declines to use it, and Matthew, who had been a collector himself, is the only one who records it.