For I was alive without the law once: but when the commandment came, sin revived, and I died.
Before being convicted by the Law, Paul was alive, that is, his sinful nature was comparatively dormant and he was blissfully ignorant of the pit of iniquity in his heart. When the commandment came, with conviction, Paul said his sinful nature became thoroughly inflamed. The more he tried to obey, the worse he failed. He died as far as any hope of achieving salvation by his own character or efforts were concerned. He died to any thoughts of his own inherent goodness. He died to any dream of being justified by law-keeping.