MATT. XVII. 22, 23. "And while they abode in Galilee, Jesus said unto them, The Son of Man shall be betrayed into the hands of men, and they shall kill Him, and the third day He shall be raised again. And they were exceeding sorry."
THAT is, to hinder their saying, "wherefore do we abide here continually," He speaks to them again of the passion; on hearing which they had no wish so much as to see Jerusalem. And it is remarkable how, when both Peter had been rebuked, and Moses and Elias had discoursed concerning it, and had called the thing glory, and the Father had uttered a voice from above, and so many miracles had been done, and the resurrection was at the doors (for He said, He should by no means abide any long time in death, but should be raised the third day); not even so did they endure it, but were sorry; and not merely sorry, but exceeding sorry.
Now this arose from their being ignorant as yet of the force of His sayings. This Mark and Luke indirectly expressing said, the one, "They understood not the saying, and were afraid to ask Him:"the other, "It was hid from them, that they perceived it not, and they feared to ask Him of that saying."
And yet if they were ignorant, how were they sorry? Because they were not altogether ignorant; that He was to die they knew, continually hearing it, but what this death might be, and that there would be a speedy release from it, and that it would work innumerable blessings, as yet they knew not clearly; nor what this resurrection might be: but they understood it not, wherefore they grieved; for indeed they clung very earnestly to their Master.
"And when they had come to Capernaum, they that received the didrachma came to Peter, and said, Does not your Master pay the didrachma?"
And what is this "didrachma?" When God had slain the firstborn of the Egyptians, then He took the tribe of Levi in their stead. Afterwards, because the number of the tribe was less than of the firstborn among the Jews, for them that are wanting to make up the number, He commandeda shekel to be contributed: and moreover a custom came thereby in force, that the firstborn should pay this tribute.
Because then Christ was a firstborn child, and Peter seemed to be first of the disciples, to him they come: their way being, as I suppose, to exact it in every city; wherefore also in His native place they approached Him; for Capernaum was accounted His native place.
And Him indeed they dared not approach, but Peter; nor him either with much violence, but rather gently. For not as blaming, but as inquiring, they said, "Does not your Master pay the didrachma?" For the right opinion of Him they had not as yet, but as concerning a man, so did they feel; yet they rendered Him some reverence and honor, because of the signs that went before.
Source: Homilies on the Gospel of St. Matthew (New Advent)