What was the purpose of the priesthood of Israel?
The priesthood of Israel was established to serve as a go-between, bringing salvation to the pagan Gentiles. Israel was to be a light to the nations, so that God's salvation would reach the ends of the earth, as prophesied in Isaiah. This was the whole idea of their priestly role.
Les explains that Isaiah 49:6 shows God's servant is to raise up the tribes of Jacob and restore Israel, but also to be a light to the Gentiles, extending salvation to the ends of the earth. Les teaches that this was the whole idea of the priesthood of Israel—to be the go-between to bring salvation to pagan Gentiles. Israel's priestly calling was not exclusive; they were to mediate God's salvation to the nations, as seen in the prophecy that the Messiah would bring forth judgment or rule to the Gentiles.
And he said, It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth.