What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
8 But sin, taking occasion by the commandment, wrought in me all manner of concupiscence. For without the law sin was dead.
9 For I was alive without the law once: but when the commandment came, sin revived, and I died.
10 And the commandment, which was ordained to life, I found to be unto death.
11 For sin, taking occasion by the commandment, deceived me, and by it slew me. Rom7:7-11
Saul earnestly sought justification by obeying the law. He understood what was entailed in obeying the ten commandments. He must obey the law relating to the inner man, the law no one but he and God need know he broke. Some will excuse that law as trivial, it is not so important, the main things are do not murder, steal, commit adultery etc. Paul knew better. For because of that law, Paul stated the commandment that was ordained to life he found to be unto death. It would be a hard thing for a young teenager who had just reached puberty to be told, if they have any impure thoughts it shows they have not been saved, for they have failed the standard of righteousness. Be tough for an adult too!