The backbone of the latter verses of 2 Corinthians 5 is neither Isaiah 53 nor 49, but the question of reconciliation. The word, either in noun or verb form, is found four times in verses 18-20. Reconciliation here presupposes an alienation or separation between man and God. It is this that has to be dealt with.The backbone of 2 Cor 5 is not Isaiah 53, but Isaiah 49, which is what Paul quotes. It is about God's fulfillment of his covenant promises to bless all nations through Israel. Paul is saying that the church in Christ is the means by which God is fulfilling these promises hence why "we become the righteousness of God in the Messiah." The righteousness of God refers to his covenant faithfulness.
Reconciliation usually requires a mediator; Job felt the need for such a one in Job 9:33. But part of the job of a mediator is to resolve the differences between the two parties. But mediation requires a satisfaction to be made to the offended party. We see this is the book of Philemon. Here we have an offended party, Philemon, whose servant has run away from him, perhaps stealing some goods as he went; an offending party, Onesimus, and Paul who is attempting to mediate between them. Onesimus needs to return to his master, but fears the sanctions that may be imposed upon him if he does so. Paul takes these sanctions upon himself: ‘But if he has wronged you or owes anything, put that on my account. I, Paul, am writing with my own hand. I will repay…..’ (Philemon 18-19). Whatever is wanting to propitiate Philemon’s anger against his servant and to effect reconciliation, Paul the mediator willingly agrees to provide. In the same way, the Lord Jesus has become a Mediator between men and God (1 Timothy 2:5). How is this done? Our Lord has willingly taken all the sins of His people upon Himself and paid the penalty in full.
The way to reconciliation is now open, so Paul's preaching is along those lines '.......As though God were pleading through us, we implore [you] on Christ's behalf, be reconciled to God.' The word 'you' is not found in any Greek manuscript SFAIK. This is a sample of Paul's teaching. Guilty sinners can now be reconciled to God. How? 'FOR He made Him who knew know sin to be sin that we might become the righteousness of God in Him.' It is this act that has made this reconciliation possible.
When you say, "The righteousness of God refers to His covenant faithfulness," you offer no Scriptural justification of the statement. The righteousness of God, as Luther discovered, is the righteousness and obedience of Christ imputed to believers through His death (Romans 5:6, 19; 2 Peter 1:1). Theologians talk of our Lord's 'active' and 'passive' obedience, and that's not wrong, but in fact His life and death were all of a part; He was obedient unto death (Philippians 2:8).
'By His wounds we are healed.' We were dead in trespasses and sins; Christ made us alive (Ephesians 2:4-6). 'He was wounded for our transgressions; He was bruised for our iniquities.' He took the punishment that we deserved.Regarding Isaiah 53, I have already pointed out on this thread that the logic of the text contradicts penal substitution. On penal substitution, it would read "by his wounding we avoid being wounded" but what the text actually says is "by his wounds we are healed." By his death the dead are brought back to life. And it is clear from the immediate context of Isaiah 53 and from the longest NT commentary on Isaiah 53, 1 Peter 2:19-25, that the suffering of the Servant is unjust.
Coming to 1 Peter 2:19-25, as I wrote in post #115, certainly it was the sinful actions of men that brought Him to the cross, but they were fulfilling the purpose and good pleasure of God (Isaiah 53:10; Acts of the Apostles 4:28; cf. Genesis 50:20) and these were not sinful but righteous. In 1 Peter 2:23-24, we are told that the Lord Jesus 'committed Himself to Him who judges justly. He Himself bore our sins in His own body on the tree......' So we cannot say that God was unjust at the cross. Again, I'm reminded of Genesis 50:20. 'But as for you, you meant evil against me; but God meant it for good.....'
Galatians 3:13. Christ has redeemed us from the curse of the law, having become a curse for us......' The Galatian churches were largely Gentile, and the major purpose of the letter was to encourage them not to espouse Jewish teachings. Therefore the suggestion that Paul had Israel in mind in this verse is silly. To be sure, through His union with the believer Christ suffers the curse along with His elect (Galatians 2:20), but not with Israel after the flesh. And I've already covered the question of the justice or otherwise of Christ's sufferings.And Galatians 3 I have also responded to on this thread already. Jesus suffers the curse along with Israel (not as Israel's substitute) and he suffers it unjustly, so that the curse would be reversed by his resurrection.