Answer:
In the Old Testament, Jews were required to sacrifice animals annually to receive forgiveness for their sins from God. Because this was ineffective, God decided that to give permanent forgiveness to all people, his only son, Jesus would come to earth as a human, die a horrific death and rise again. Jesus voluntarily gave up his life by being crucified on a cross, thus being a sacrifice for all humans to receive forgiveness from God if they believe in Jesus's ressurection. This is the pillar of Christian beliefs.