It is good - It is right; or it is better. This verse is an explanation or enlarged specification of the meaning of the former.
To eat flesh - That is, such flesh as the "Jewish" convert regarded as unclean; Romans 14:2.
Nor to drink wine - Wine was a common drink among the Jews, and usually esteemed lawful. But the Nazarites were not allowed to drink it Numbers 6:3, and the Rechabites Jeremiah. 35 drank no wine, and it is possible that some of the early converts regarded it as unlawful for Christians to drink it. Wine was moreover used in libations in pagan worship, and perhaps the Jewish coverts might be scrupulous about its use from this cause. The caution here shows us what should be done "now" in regard to the use of wine. It may not be possible to prove that wine is absolutely unlawful, but still many friends of "temperance" regard it as such, and are grieved at its use. They esteem the habit of using it as tending to intemperance, and as encouraging those who cannot afford expensive liquors. Besides, the wines which are now used are different from those which were common among the ancients. That was the pure juice of the grape. That which is now in common use is mingled with alcohol, and with other intoxicating ingredients. Little or none of the wine which comes to this country is pure. And in this state of the case, does not the command of the apostle here require the friends of temperance to abstain even from the use of wine?
Nor anything - Any article of food or drink, or any course of conduct. So valuable is peace, and so desirable is it not to offend a brother, that we should rather deny ourselves to any extent, than to be the occasion of offences and scandals in the church.
Stumbleth - For the difference between this word and the word "offended," see the note at Romans 11:11. It means here that by eating, a Jewish convert might be led to eat also, contrary to his own conviction of what was right, and thus be led into sin.
Or is made weak - That is, shaken, or rendered "less stable" in his opinion or conduct. By being led to imitate the Gentile convert, he would become less firm and established; he would violate his own conscience; his course would be attended with regrets and with doubts about its propriety, and thus he would be made "weak." In this verse we have an eminent instance of the charity of the apostle, and of his spirit of concession and kindness. If this were regarded by all Christians, it would save no small amount of strife, and heart-burnings, and contention. Let a man begin to act on the principle that peace is to be promoted, that other Christians are not to be offended, and what a change would it at once produce in the churches, and what an influence would it exert over the life!

It is good neither to eat flesh, etc. - The spirit and self-denying principles of the Gospel teach us, that we should not only avoid every thing in eating or drinking which may be an occasion of offense or apostasy to our brethren, but even to lay down our lives for them should it be necessary.
Whereby thy brother stumbleth - Προσκοπτει, from προς, against, and κοπτω, to strike, to hit the foot against a stone in walking, so as to halt, and be impeded in one's journey. It here means, spiritually, any thing by which a man is so perplexed in his mind as to be prevented from making due progress in the Divine life. Any thing by which he is caused to halt, to be undecisive, and undetermined; and under such an influence no man has ever yet grown in grace and in the knowledge of Jesus Christ.
Or is offended - Η σκανδαλιζεται, from σκανδαλον, a stumbling-block; any thing by which a person is caused to fall, especially into a snare, trap, or gin. Originally the word signified the piece of wood or key in a trap, which being trodden on caused the animal to fall into a pit, or the trap to close upon him. In the New Testament it generally refers to total apostasy from the Christian religion; and this appears to be its meaning in this place.
Or is made weak - Η ασθενει, from α, negative, and σθενος, strength; without mental vigor; without power sufficiently to distinguish between right and wrong, good and evil, lawful and unlawful. To get under the dominion of an erroneous conscience, so as to judge that to be evil or unlawful which is not so. The two last terms are omitted by two excellent MSS. (the Codex Alexandrinus and the Codex Ephraim), by the Syriac of Erpen, the Coptic and the Ethiopic, and by some of the primitive fathers. It is very likely that they were added by some early hand by way of illustration. Griesbach has left them in the text with a note of doubtfulness.

It is good neither to eat flesh,.... Any sort of flesh, even that which is not forbidden in the law, rather than offend a weak brother; and the apostle determines for himself, that he would not, where there was any danger of doing this, 1-Corinthians 8:13.
Nor to drink wine; not only the wine of libations to Heathen deities, but wine in common; which was not prohibited by the law of Moses, but in the case of a Nazarite, and of vows:
nor anything, be it what it will,
whereby thy brother stumbleth. The Syriac version reads, "our brother"; anyone that stands in such a spiritual relation to any of us; and for which reason care should be taken, that no stumblingblock, or occasion to fall, should be put in his way; particularly that Christian liberty in things indifferent be not unseasonably and imprudently used, and so become a means of stumbling and staggering to weak minds:
or is offended; to that degree, as to censure and judge him that eats, as an impious person, and a transgressor of the law; with whom he cannot keep his communion, but withdraws himself from it, and is even tempted to drop his profession of the Christian religion entirely, being ready to think it is not right, since contrary to the law of Moses:
or is made weak; more weak in the faith than he was before, and his love is weakened and grows very cold and indifferent to his Christian brethren, that can take and use a liberty which he cannot. These two last phrases are not in the Syriac and Ethiopic versions, nor in the Alexandrian copy, though in others, and are used for the sake of explanation and amplification.

It is good not to eat flesh, nor to drink wine, nor any thing--"nor to do any thing"
whereby--"wherein"
thy brother stumbleth, or is offended, or is made weak--rather, "is weak." These three words, it has been remarked, are each intentionally weaker than the other:--"Which may cause a brother to stumble, or even be obstructed in his Christian course, nay--though neither of these may follow--wherein he continues weak; unable wholly to disregard the example, and yet unprepared to follow it." But this injunction to abstain from flesh, from wine, and from whatsoever may hurt the conscience of a brother, must be properly understood. Manifestly, the apostle is treating of the regulation of the Christian's conduct with reference simply to the prejudices of the weak in faith; and his directions are to be considered not as prescriptions for one's entire lifetime, even to promote the good of men on a large scale, but simply as cautions against the too free use of Christian liberty in matters where other Christians, through weakness, are not persuaded that such liberty is divinely allowed. How far the principle involved in this may be legitimately extended, we do not inquire here; but ere we consider that question, it is of great importance to fix how far it is here actually expressed, and what is the precise nature of the illustrations given of it.

Thy brother stumbleth - By imitating thee against his conscience, contrary to righteousness. Or is offended - At what thou doest to the loss of his peace. Or made weak - Hesitating between imitation and abhorrence, to the loss of that joy in the Lord which was his strength.