This is one of the questions posed and answered by Richard Bewes in his little book The Top 100 Questions.
Put slightly differently, the question is: What does it mean to say that Jesus Christ died ‘for’ me?
The most fundamental answer to this question, says Bewes, lies in the idea of ‘penal substitution’. Christ was the only person qualified to take upon himself the penalty of separation from God (Romans 6:23), and he himself declared that he had come to give his life in the place of many (Mark 10:45).
This central truth is developed in a number of images:-
1. The Cross means penalty paid – redemption (Ephesians 1:7). This is the language of the slave market. A price – Christ’s blood – has been paid for us to be set free, 1 Peter 1:18f.
2. The Cross means wrath averted – propitiation (Romans 3:25; 1 John 2:2). This is the language of the temple, and of sacrificial offering. God’s holy antagonism to human rebellion brings us all under judgment. God has intercepted his own judgment, in the person of his Son, and his wrath is averted.
3. The Cross means righteousness exchanged – justification (Romans 3:21-26). This is the language of the law courts. How could I, a sinner, be treated as if I had never sinned? Only by Christ taking making place, and being treated as the sinner, so that his righteousness can be accredited to me.
4. The Cross means relationship restored – reconciliation (Rom 5:9-11; 2 Cor 5:19-21). This is the language of family. But our reconciliation required that Christ be ‘made sin for us’. Only by this means could it be possible for us to be adopted back into God’s family.
Four wonderful truths – and the doctrine of penal substitution lies behind all of them.