Adam Clarke on 1 Corinthians 8:12

But when ye sin so against the brethren - Against Christians, who are called by the Gospel to abhor and detest all such abominations.

Ye sin against Christ - By sending to perdition, through your bad example, a soul for whom he shed his blood; and so far defeating the gracious intentions of his sacrificial death. This is a farther intimation, that a person for whom Christ died may perish; and this is the drift of the apostle's argument.