According to Paul, salvation is only possible by believing. We are saved by God's grace through faith in Jesus Christ (Ephesians 2:8). But, how do we receive that faith?
God uses His Word to reach people and to bring them to faith in Jesus Christ, to help believers grow in faith, and to lead believers through this life.
In the Old Testament, sacrifice meant that a life had to be taken. This points to the life and death of Jesus Christ, which in a sense had to be taken in order for us to be united with God.