Scholars debate who it is that is speaking in Isaiah 50:4-9 and the rest of the so called "suffering servant" passages. Is this Isaiah speaking? Is it a prophetic successor of Isaiah? Should we understand this as the collective voice of Israel as a nation that suffers as God's servant? Is this a prophecy about the coming Messiah, about Jesus?
Obviously, for those of us who believe that Jesus is the Messiah, it is easy to jump to that last option. So many of the images found in Isaiah 49-53 seem to fit Jesus so well. While I am not convinced that Isaiah (or the disciple of his who wrote these words) had Jesus in mind, I am convinced that Jesus must have often had these words in mind throughout his life and ministry, especially as he drew nearer to the cross. In other words, I don't think it is so much that Jesus perfectly fulfilled some pre-existing expectation of what it meant to be Messiah (in fact, I am quite certain he was constantly exploding the pre-existing notions of Messiah) as much as he found his understanding of who he was as the Messiah in places where no one else was looking. While others were looking for Moses, Elijah, and David all rolled into one, Jesus found his Father calling him to stand in the line of rejected prophets like Isaiah, Jeremiah, and Ezekiel.
It is fitting then that Isaiah 50 is one of the texts for Palm Sunday. Those waving their palm branches welcome Jesus into Jerusalem as that Moses/Elijah/David figure. But this celebration only lasts as long as the crowd fails to see Jesus as he sees himself, as long as they see him as one who has come to save by power when, in fact, he has come to save by suffering and weakness. It takes less than a week for the chants of "Hosanna" to become chants of "Crucify him".
The role of prophet and disciple as described in Isaiah 50 and as modeled by Jesus in his journey to the cross serves as a sharp contrast to the fickle crowds of Palm Sunday. The crowds celebrate only as long as things are going their way. In contrast, the prophet/disciple has a face set like flint, a determination that can be compared only to the solid, steadfastness, and unwavering nature of rock. The prophet/disciple is certain that the Lord is his present helper even when he is struck and spit on. The prophet/disciple is confident that he will be vindicated even as everyone goes against him because he hears and is sustained by word of the Lord every morning.