Romans 3:25

God presented him as a sacrifice of atonement, through faith in his blood. He did this to demonstrate his justice, because in his forbearance he had left the sins committed beforehand unpunished—

(v25, NIV)

Jesus is presented by God as an atoning sacrifice. Apparently, atonement is to make amends for injury or wrong done. If Jesus was a sacrifice of atonement, what is the wrong done? Certainly, Jesus didn't do anything wrong because he is the pure spotless lamb. In addition, God presented him as a sacrifice, and it wouldn't really be a sacrifice if he was atoning for something he did himself. Instead, he is the atoning sacrifice for those whom God chooses to save. This atonement is for our sins. As a result, payment is required for all this wrong doing that we do. Jesus is the perfect sacrifice that atones for our sins. He pays the price that we could not pay and we receive his perfect life. This is what he did for us and we did not do anything to merit this. This is a free gift which we receive.