Answer
In the teachings of the Bible, different methods are used from time to time in order to impart the lesson of salvation. In Old Testament times, God used the Law to reveal his grace, and in the New Testament he accomplishes this through the Son. All God's works are consistent. He used the Israelite's laws as a type so that we could understand his will. Of course, the Law and all of the Old Testament rituals themselves don't have redemptive power, even though they're all true teachings. Still, they gave the Israelites the ability to understand God's will for their day. In the time of the New Testament, God directly revealed himself in the Son, coming to earth to complete the work of salvation. And the New Testament is completely consistent with the Old; the basic principles of God's grace didn't change. To put it simply, Christ, as God's righteous Son, had to fulfill God's holy demands on our behalf, so that we could return to God and be reconciled to him. Additionally, as the Son of God, Christ was substituted for our sins, freeing us from sin's curse. So, salvation always has two parts: fulfilling God's requirements, and rescuing humanity. Christ is the only Savior who can fulfill these two aspects.
Answer by Dr. Stephen Chan
Dr. Stephen Chan is the Associate Professor of Theology and Religious Studies at Seattle University