"from among all those who have died." The expression "the dead" describes all dead people together in the underworld. To raise someone from among them speaks of causing that person to become alive again.
Christ in his role of leader and protector of those who believe in him is spoken of as if he were a shepherd of sheep. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here "blood" stands for the death of Jesus, which is the basis for the covenant that will last forever between God and all believers in Christ. (See: [[rc://en/ta/man/jit/figs-metonymy]])