‘How’ questions are always very interesting questions, because a lot of mechanistic questions (how things work) tend to be speculation. So this may involve some guesswork. And it seems this is what Paul is trying to explain in a number of his letters! I no real formulated answer, but I’d be interested to break down the concept with you and the others.
Yes, only Christ did die for our sins. We do not die for our sins; we die to our sin. Because He died for them, we can die to them. By His death, we are set free from the power sin has over us. Through His resurrection, we too have life.
Now if we have died with Christ, we believe that we will also live with him. [Rom. 6:8]
But the how remains, does it not? How do we ‘pick up our cross’ or die to self? How is His death applied to us? How are we grafted ‘into Christ’? What does it even mean for us to be ‘in Him’? (Fun exercise: count how many times Paul uses that phrase in Ephesians alone!)
It’s a similar question to Nicodemus’ in John 3, is it not, when Jesus tells him he needs to be ‘born again’.
“How can a man be born when he is old? Can he enter a second time into his mother’s womb and be born?”
Jesus doesn’t really answer the how question there…at least not that I can see. What He tells Nic, in my mind, just invites another how question. Jesus essentially says that one must be ‘born of water and the Spirit’. Nicodemus follows this up by saying (and echoing my own question!),
“How can these things be?”
Jesus then seems to ridicule him (though I doubt He said it with an attitude of ridicule…or maybe he did??)…
Are you the teacher of Israel and yet you do not understand these things?
Paul attempts to understand and explain these things in his various letters. For example, in Colossians:
In him also you were circumcised with a circumcision made without hands, by putting off the body of the flesh, by the circumcision of Christ, having been buried with him in baptism, in which you were also raised with him through faith in the powerful working of God, who raised him from the dead. And you, who were dead in your trespasses and the uncircumcision of your flesh, God made alive together with him, having forgiven us all our trespasses, by cancelling the record of debt that stood against us with its legal demands. This he set aside, nailing it to the cross. He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him. [Col 2:11-15]
He does try to explain some of the mechanisms in there, but it doesn’t seem he can fully explain them.
Is this opening the question up at all in a helpful direction? I’d be curious to hear your own reflections! It’s been refreshing for me to type this out and think though, so thank you for bringing the question in the first place.