When preachers compare the response of the crowd on Palm Sunday (“Hosanna!”, Mk 11:9; Mt 21:9; “Blessed is he who comes in the name of the Lord”, Lk 19:38) to that of the crowd just a few days’ later (“Crucify him!”, Mk 15:13; Lk 23:21; Jn 19:15) they often explain this in terms of fickleness (“How quickly they change their minds about Jesus!”).  I’ve done it myself.

So also in the hymn ‘My Song is Love Unknown’:

Sometimes they strew his way/And his sweet praises sing…Then “Crucify!” is all their breath…

But it’s not at all clear that the crowd who acclaimed Jesus’ triumphal entry into Jerusalem was the same group of people who called for his execution.  The former were probably mainly pilgrims from Galilee; they had followed Jesus into Jerusalem (Mt 20:29).  The latter were mostly from Jerusalem itself.

In any case, the responses of both crowds was based on different understandings of Jesus’ mission.  The crowd shouting “Hosanna!” may have been motivated by nationalistic fervour, whereas the people calling for Jesus’ death had been incited by those who were falsely accusing him of blasphemy.

Based on this article by Andreas J. Köstenberger and Justin Taylor.

See also this, by Ian Paul.