In the first four chapters, Paul explains HOW we are saved by Jesus. In summary, he writes that we are saved by faith. Those who believe Jesus dies for their sin, and that Jesus is the substitutionary punishment for us, are saved. After explaining how to be saved, the Apostle Paul changes the subject in chapter five. He answers a very important question, which is, “WHY are we saved?” What motivates God to save us? Why, does God choose to save people. Paul addresses God’s motive for salvation. The short answer to Paul’s question is simple. The reason we are saved is because of God’s love. We know the answer because we are familiar with what Jesus said to Nicodemus. “For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.” God loves the world. That’s why.
Jesus is the perfect Lamb of God who has no blemish. Our atonement may only come from someone who does not deserve the punishment. In other words, Jesus cannot take our punishment if He also deserves punishment (otherwise, He will have to die twice, once for Himself and once for us). Isaiah rightly prophecies that the atoning sacrifice of the Lamb of God is made with an innocent Lamb without a blemish. He is pure, holy, and righteous.