That uniqueness is made especially clear in the astonishing fourth servant song where the servant is now described as one who has "borne our infirmities and carried our diseases," who "was wounded for our transgressions, crushed for our iniquities" (53:4-5). Note the repetition of the word "crushed" in 42:4 and 53:5. The silent yet relentless servant will stop at absolutely nothing to bring justice to the nations. But justice will come, says Isaiah, only when the servant gives himself for his people. It is no wonder at all that early Christians read these words and found in them a true picture of the one who had died on the Jerusalem cross.
But back to Isaiah. Perhaps the question to ask is not: Who is the servant of YHWH? It might be the prophet himself, or some unnamed exile, or some wandering wise man. We will never know. But what Isaiah had in mind for the servant was surely nearly unprecedented. This servant will bring justice; make no mistake about that. But he will do so quietly, mysteriously, and finally by self-offering for all. Such a radical idea! For us Christians it has become the most radical and crucial idea in all the world.