‘Sin’ [verb] is something you do. Emphasis on ‘you’ - more about this soon
2 COR 5:10 For we must all appear before the judgment seat of Christ, so that each of us may receive what is due us for the things done while in the body, whether good or bad.
But let’s go back a few verses. This whole chapter has been about your ‘body’. Which Paul likens to a ‘tent’
2 COR 5:1 For we know that if the earthly tent we live in is destroyed, we have a building from God, an eternal house in heaven, not built by human hands
The physical body is referred to as “our earthly house of this tabernacle.” The word “tabernacle” is a metaphor used of the human body describing a “tent” that is to be taken down at the point of death.
But if you look/read closely, you’ll notice an important point, example ....
2 COR 5:6 Therefore we are always confident and know that as long as we are at home in the body we are away from the Lord.
Paul never referee to the body as ‘being him’, or, ‘who he is’. But rather that the body and ‘he’ himself are two separate entities. But more - he himself is responsible for what his body does. Paul was clear that this is a judgment of our works done in the body, or rather what ‘we’ did/do with our body.
In the light of Paul wanting to please the Lord (2 Corinthians 5:9), he here turned his attention to a judgment seat before which all believers will stand.
All ‘sin’ is done with the body. Because ‘sin’ is something you do (with/using your body). Therefore your ‘thoughts’ will not be judged. It’s crystal clear (from this chapter describing judgement) that you [only] get judged for *what you [actually] do.
All ‘sin’ is ‘in’ the body (flesh, although ‘flesh’ includes the body, it specifically means the ‘physical senses’/carnal.).
What you ‘do’ with your body depends on the ‘source’ you ‘listen’ to. This can be the flesh, or the spirit. One always leads to you (doing) ‘sin’, the other [if reborn!] results in ‘fruit’ (of the spirit). This leads to another important understanding we need ..
‘Evil’ in Hebraic thinking is a state of the ‘heart’, specifically man’s ‘unrighteous’ spirit. Evil is not sin. But it [always] results in sin. We (westerners) say you ‘do’ evil. Hebraic thinking says evil results in you doing.(something we would call evil). You are judged for what you do. And everything you do is ‘in’ [or with/using] your body.
So if you had another ‘spirit’ [say a demon] influence you, it’s still your body, and you’ll be accountable for what you did with your body. A person has to ‘submit’ [a wilful decision or choice, allow] to ‘listen’ to any source.
Therefore all “sin” is ‘in the flesh’. And in the Old Testament, it was your ‘flesh’ [body] that had to pay the penalty - (stoning).