Galatians 2:18 KJV
For if I build again the things which I destroyed, I make myself a transgressor.
The apostle is speaking specifically about the Old Testament Law.
His concern is that if after destroying the Law for righteousness by coming to Christ, he would begin again to practice that same Law as a matter of righteousness he would be rebuilding what he had destroyed and would be in transgression in doing it.
He was especially concerned because such activity could lead to some other person believing that trusting Christ was vain and he should seek righteousness only through works of the Law.
Oh how many there have been who, having met Jesus Christ and turning to Him have, some time later, returned to build again those fleshly works which they once destroyed.
• Some in returning to their former sins
• Some in returning to former practices
though not sin in themselves, become sinful because they draw them away from that which is godly.
How often too their return has led to the downfall of those they love and who love them; children and grandchildren, who follow them in the sin but never have faith in Jesus Christ.