Alma 21:9

Now Aaron began to open the Scriptures unto them, concerning the coming of Christ, and also concerning the resurrection of the dead, and that there could be no redemption for mankind, save it were through the death and sufferings of Christ, and the atonement of his blood.

Aaron began to show them the scriptures. He taught them about Christ coming. He also taught them that dead people would come back to life. He said people could only be saved because of Christ’s death and suffering. Christ’s blood paid for their sins.

So Aaron began opening the scriptures to them, teaching about the coming of Christ, about the resurrection of the dead, and that there could be no salvation for anyone except through Christ’s death and suffering—through the sacrifice of his blood.