How do we know Christ's death was for our sins?

The significance of Christ's sacrificial death is illustrated in the typology of the serpent lifted up in the wilderness, as recorded in Numbers 21:8-9. Just as the Israelites who looked at the bronze serpent were healed, so too, Christ was lifted up on the cross to provide salvation for all who believe. This understanding is affirmed in John 3:14-15, where Jesus connects His crucifixion to this Old Testament event, emphasizing that His death is the means by which sinners receive healing from the poison of sin, which was inherited from Adam.