John Calvin Commentary 1 Corinthians 8:12

"And thus, sinning against the brethren, and wounding their conscience when it is weak, ye sin against Christ." — 1 Corinthians 8:12 (ASV)

When ye sin so against the brethren, etc. For if the soul of everyone who is weak is the price of Christ’s blood, that man who, for the sake of a very small portion of meat, hurries back again to death the brother who has been redeemed by Christ, shows how contemptible the blood of Christ is in his view. Therefore, contempt of this kind is an open insult to Christ. In what way a weak conscience may be wounded has already been explained—when it is built up in what is evil (1 Corinthians 8:10), so that the individual daringly and rashly rushes further than he thinks is lawful for him.