But when ye sin so against the brethren, and wound their weak conscience, ye sin against Christ.

Now when you sin thus against the brethren, and wound their weak conscience, you sin against Christ.

Now, thus sinning against the brethren, and wounding their weak conscience, ye sin against Christ.

and thus sinning in regard to the brethren, and smiting their weak conscience, in regard to Christ ye sin;

Moreover when you thus sin against the brethren and wound their weak consciences, you are, in reality, sinning against Christ.

And in this way, doing evil to the brothers, and causing trouble to those whose faith is feeble, you are sinning against Christ.

So when you sin in this way against the brothers, and you harm their weakened conscience, then you sin against Christ.

In this way, by sinning against your fellow followers of the Lord and injuring their consciences, while still weak, you sin against Christ.

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. Hence contempt of this kind is an open insult to Christ. In what way a weak conscience may be wounded has been already explained -- when it is built up in what is evil (1-Corinthians 8:10) so as daringly and rashly to rush on farther than the individual thinks to be lawful for him.

But when ye sin so against the brethren - This is designed further to show the evil of causing others to sin; and hence, the evil which might arise from partaking of the meat offered to idols. The word sin here is to be taken in the sense of "injuring, offending, leading into sin." You violate the law which requires you to love your brethren, and to seek their welfare, and thus you sin against them. Sin is properly against God; but there may be a course of injury pursued against people, or doing them injustice or wrong, and this is sin against them. Christians are bound to do right toward all.
And wound their weak conscience - The word "wound" here (τύπτοντες tuptontes, "smiting, beating") is taken in the sense of injure. Their consciences are ill-informed. They have not the knowledge which you have. And by your conduct they are led further into error, and believe that the idol is something, and is to be honored. They are thus led into sin, and their conscience is more and more perverted, and oppressed more and more with a sense of guilt.
Ye sin against Christ - Because:
(1) Christ has commanded you to love them, and seek their good, and not to lead them into sin, and,
(2) Because they are so intimately united to Christ (see the notes at John 15:1 ff) that to offend them is to offend him; to injure the members is to injure the head; to destroy their souls is to pain his heart and to injure his cause; see the note at Matthew 10:40; compare Luke 10:16.

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.

(8) But when ye sin so against the brethren, and wound their weak conscience, ye sin against Christ.
(8) Another amplification: such offending of our weak brethren, results in the offending of Christ, and therefore do not let these men think that they have to deal only with their brethren.

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
wound their weak conscience: as before observed: it is contrary to the law of love to wound a brother; it is an aggravation of the sin to wound a weak one; what greater cruelty than to strike or beat, as the word here used signifies, a sick and infirm man? and greater still to strike and wound his conscience than any part of his body; for a wounded spirit is insupportable without divine aid and influence; and what serves most to enhance the crime and guilt is,
ye sin against Christ, who has so loved this weak brother as to die for him; and between whom there is so close an union, as between head and members; and from whence such a sympathy arises, that what is done to or against such a person, Christ takes as done to himself. The Syriac version emphatically adds, "himself".

wound their weak conscience--literally, "smite their conscience, being (as yet) in a weak state." It aggravates the cruelty of the act that it is committed on the weak, just as if one were to strike an invalid.
against Christ--on account of the sympathy between Christ and His members (Matthew 25:40; Acts 9:4-5).

Ye sin against Christ - Whose members they are.