For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God.
2 Corinthians 5:21
There are three aspects of our salvation that strike me from this verse. The first is God's sovereignty over our salvation. God made "him to be sin" (talking about Jesus) "for our sake" (talking about us). God did the sovereign work of decreeing our salvation in Christ. He did it for us and by "making" Jesus go to the cross with our sins. It was a sovereign work of God, not a tragic mistake or miscarriage of justice. Jesus meant to die for us, telling His disciples in advance exactly what would happen in His death and resurrection, carrying the weight of our sin upon Himself in obedience to the Father's own plan.
Secondly, Jesus was sinless. No sinner can be our savior. He "knew no sin". God "made him to be sin", but Jesus in His own person never sinned. His perfect life was offered up for our sin so that His righteousness could be given to us. That leads to a third observation.
Jesus is our substitute. He died for us. This is the great exchange. Jesus took our sins and gave us His righteousness. He took God's wrath on the cross and brought us peace. He was made to be sin so that we might become the righteousness of God. Truly believing the gospel changes us... from the worst of sinners to true saints of God in Christ Jesus!