By sinning against your brothers in this way and wounding their weak conscience, you sin against Christ.
12. When ye sin so against the brethren, etc. For if the soul of every one that 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.
The apostle, having granted, and indeed confirmed, the opinion of some among the Corinthians, that idols were nothing, proceeds now to show them that their inference from this assumption was not just, namely, that therefore they might go into the idol-temple, and eat of the sacrifices, and feast there with their heathen neighbours.
Commenting on 1 Corinthians 8:7-13
But when ye sin so against the brethren,.... Through sitting at meat in an idol's temple, and thereby violating the new commandment of love; by which saints are obliged to love one another as brethren, and take care to do nothing that may hurt and prejudice one another's peace and comfort, it being an incumbent duty upon them by love to serve one another: and...