What Does the Old Testament Say about the Nature and Role of the Messiah?

Question about what the Old Testament says about the nature and role of the Messiah and whether it leaves open the option that Jesus is God and a man can die for our sins.

• In light of hearing a Jewish person say he isn’t a Christian because he doesn’t believe Jesus is God or that a man can die for our sins, what does the Old Testament say about the nature and role of the Messiah that the Jews are/were waiting for?