Charles Spurgeon Commentary Matthew 17:10

"And his disciples asked him, saying, Why then say the scribes that Elijah must first come?" — Matthew 17:10 (ASV)

One by one, the difficulties of the disciples are stated to their Lord, and their solution is soon given. One of these concerned Elijah, and since he had been before them just now, they were led to mention it. “Why then say the scribes that Elias must first come?” This is the report of men who have studied our Scriptures: that Elias comes before the Lord’s appearing. No doubt it staggered their minds when it was put to them in such a logical fashion as this:

Messiah cannot come until Elijah has appeared. Elijah has not appeared. Therefore, Jesus is not the Messiah.