It’s got to do with Paul’s efforts to attain right standing with God by adherence to the Law, IOW, works.
All the effort he made, he realized, means nothing compared to being found in Christ and having Christ’s righteousness imputed to him through faith is far better than having his own which he tried to attain by works.
All his technical sinless perfection under the law means nothing. It did not give him the righteousness he sought after.
It’s being found *in Christ* is all that matters, thus not having a righteousness of his own.
It seems we are trying to deal with some hypothetical situations, than can be very difficult to explain on an Internet forum like this. I will try, however. First, let me say, that God is the ONLY one who truly knows the heart, whether a person is truly saved or not. We only see from the outside.
Now, when I was 21, I became a born again Christian. His righteousness was imputed to me. My life began to miraculously change. That’s how I knew it was real. Hypothetically speaking again, I would say if a person claims to have become a born again Christian, and yet has no change in his life, is he truly saved? Hypothetically, I would say the answer is probably not, but only God knows for sure.
Once I had His righteousness imputed to me, it was a once and forever experience. The relationship has been permanently established. Now, I had two natures in me, God’s imputed nature and the old sin nature, at war with each other, both fighting for dominance. Sometimes I have victory over sin, and sometimes I don’t, but the relationship is never broken. We are never to use our relationship as an excuse for wickedness, but sometimes we still sin, which harms fellowship with God, but not the relationship. That’s when we do a 1 John 1:9, and confess. It restores the fellowship, but the relationship was always there.
Now, can a true born again Christian fall into some bad sinning. Hypothetically, I would say it is possible, but I would also say that if they do, God may hypothetically kill them. It’s possible that God will not long tolerate a true Christian bringing disrespect to His name. Doesn’t mean their relationship has ended, but their life on earth might, hypothetically of course. That is what I think is the sin unto death. It refers to physical death, not spiritual death. Remember Ananias and Sapphira. Hypothetically, true Christians, who sinned, and were removed from the earth. Hypothetically, they were saved, but were still taken out. I feel that if a true Christian wants to lead a long, fruitful, productive life, he should do his best to stay on the straight and narrow, not to get saved, but because he is saved. I hope this might help. 😁👍😇