Why did Paul consider his former law-keeping worthless?
Paul counted his former law-keeping worthless because he came to see that the work of the cross had become preeminent. Righteousness and salvation come only through faith in Christ's finished work, not through law, temple, or Old Testament observance. His former religious zeal, even as a law-keeping Jew, could not justify him.
Les explains that Paul had been a religious Jew par excellence, a law-keeping Jew and religious zealot, even killing people because they accepted something contrary to the law. But when Paul suddenly realized that all of that counted for nothing, because the work of the cross had now become preeminent, he saw that it is only through faith in the finished work of the cross that sinners can be saved. Paul then says that if he builds again the things he destroyed, he makes himself a transgressor. To go back and put his converts under the law and command them to keep circumcision would be rebuilding what he had torn down.
For if I build again the things which I destroyed, I make myself a transgressor.
More Questions
What did Paul do as a law-keeping Jew before he became a Christian?
Before his conversion, Paul as a law-keeping Jew killed people because they accepted something contrary to the law.
What did Paul do to people who accepted teaching contrary to the law?
As a law-keeping Jew, Paul killed people because they were accepting something contrary to the law, making him a religious zealot.