Charles Ellicott Commentary Matthew 21:4

"Now this is come to pass, that it might be fulfilled which was spoken through the prophet, saying," — Matthew 21:4 (ASV)

All this was done—The Evangelist returns to the formula of Matthew 1:22. Literally, all this has come to pass. The words are his comment on the act. At the time, as we find from John 12:16, the disciples did not understand its significance as connected with the prophecy that follows. The purpose lay in the mind of their Master, not in theirs. It is significant that, as John records, neither Mark nor Luke alludes to the prophecy.