Romans 7:14 — For we know that the law is spiritual: but I am carnal, sold under sin.
If the law is good, why can't it bring holiness? Because I am carnal (Romans 8:3).
The law is spiritual (verse 14).
There is nothing good in the flesh (verse 18).
So there's a result — when I would do good, evil is present (verse 21).
spiritual = holy, righteous and good (verse 12). Invisible and powerful — originating with God and in harmony with His character.
carnal = fleshly (in ethical, as opposed to material, sense)
sold under = fully dominated by — refers to the futility of the law as a means of deliverance.
Verse 14 is the end of Paul's answer to the question in verse seven and an introduction to the rest of the chapter.