I believe that Christ is the Propitiation for the sins of the whole world. This points to Christ (Christ's identity). He is this Propitiation. Here I agree with Justin Martyr's use of the "human family". I view our sins being laid upon Christ as speaking of the sins of mankind (as @charity pointed out, Sin as the root). But I do not believe that we are forgiven of our sins and then "born again". This new birth is how we are forgiven (dead to sin, alive in Christ).It isn't, but we press on.
So do I (Proverbs 17:15). That is one of the two reasons that God Himself, in the Person of Jesus Christ, came to earth to shoulder the burden of our sin and to pay the penalty of it. The other reason, of course, is found in Ecclesiastes 7:22. But none of that abates the force of verses like Nahum 1:3.
But Christ died for the ungodly, when we were still 'without strength' (Romans 5:6). The new birth comes after and as a result of, Christ's propitiation. Christ did not come to save the righteous, but sinners, .
In that case there is no need for Christ to suffer and die, if people are justified 'apart from the law,' and it would be an abomination to God if it happened. That is a misunderstanding of Romans 3:21, as Romans 3:31 explains. Details on request. Got to run.
So also it is written, “The first man, Adam, became a living soul.” The last Adam became a life-giving spirit.
It seems that we approach God's righteousness from two different angles and come up with two very different conclusions.