John Calvin Commentary 1 Timothy 1:8

"But we know that the law is good, if a man use it lawfully," — 1 Timothy 1:8 (ASV)

Now we know that the law is good. He again anticipates the slander which they heaped upon him; for, whenever he resisted their empty display, they seized on this shield for their defense: “What then? Do you wish to have the law buried, and erased from human memory?”

To refute this slander, Paul acknowledges that “the law is good,” but contends that we are required to make a lawful use of it. Here he argues from the use of cognate terms, for the word lawful (legitimus) is derived from the word law (lex). But he goes still further and shows that the law agrees excellently with the doctrine which it teaches; and he even directs it against them.