From my blog:
We learn in the Scriptures two things that the Lord Jesus became on our behalf. He became sin ‘for us’ (2 Corinthians 5:21), and He became a curse ‘for us’ (Galatians 3:13). First, He became sin. ‘For He made Him who knew no sin to be sin for us that we might become the righteousness of God in Him.’ So God the Father made the sinless Christ to be sin on our behalf. What does this mean? Well, it does not mean that Christ was made a sinner; He was never that! It means that all the sins of God’s elect were imputed to Christ– that is, laid to His account (c.f. Isaiah 53:6), and He has paid the penalty for them (Isaiah 53:5). At the same time, His perfect righteousness and obedience to His Father’s will are credited to us who believe. This is what Luther termed the ‘Great Exchange.’ The sinless One made sin, and sinners made righteous through the cross.
It has been suggested that Christ was not made ‘sin’ in 2 Cor. 5:21, but a ‘sin offering.’ There are three reasons why this suggestion should be rejected:
Firstly, hamartia, the Greek word translated ‘sin’ never means ‘sin offering’ in the New Testament, though it sometimes does elsewhere.
Secondly, hamartia occurs twice in the verse, and it would be strange if it had two meanings in one sentence; but to say, “God made Him who knew no sin offering to be a sin offering for us” makes no sense.
Thirdly, in John 3:14, the Lord Jesus declares, “As Moses lifted up the serpent in the wilderness, so the Son of man must be lifted up……” The reference is, of course, to Numbers 21:8-9, where Moses made a ‘fiery serpent,’ lifted it up on a pole, and everyone who looked upon it was cured of snake-bite. The serpent is clearly some sort of type of the Lord Jesus, but what sort? Well where do we see in Scripture a red, fiery serpent? Well in Revelation 12:3, we are introduced to ‘A great fiery red dragon’ who, in verse 9, is seen to be the serpent, alias Satan himself. So how is Satan a type of Christ? He is a type of Christ made sin for us. The Lord Jesus manifested to destroy the works of the devil (1 John 2:8). The primary satanic work was the luring of mankind into sin. Christ was made the very epitome of sin for us, figured by the brazen serpent, and paid the penalty of His people’s sin in full, so that ‘the accuser of our brethren…..has been cast down’ (Revelation 12:10). Satan can no longer accuse Christians of sin because Christ has taken away their sin debt, nailing it to the cross (Colossians 2:14) marked tetelestai, ‘Paid in Full’ (John 19:20; c.f. Matthew 17:24). Therefore ‘Who shall bring a charge against God’s elect? It is God who justifies; who is he who condemns?’ (Romans 8:33-34).