Romans 14:15

For if because of meat thy brother is grieved, thou walkest no longer in love. Destroy not with thy meat him for whom Christ died.

With regard to how the weak brother may be grieved, Greathouse has:

For one thing, it will pain his overly sensitive conscience to see you do what he (however wrongly) regards as sinful. But the real damage occurs when he is emboldened by your example to do what he believes God has forbidden him to do. He who eats with a bad conscience is a waverer who is condemned by his doubts.[14]

Thou walkest no longer in love ... is a serious charge. The Christian's credential of the hope of glory lies specifically in this, that he shall love the brethren. As an apostle said,

We know that we have passed out of death into life, because we love the brethren. He that loveth not abideth in death (1 John 3:14).

The so-called fault, therefore, of setting a brother at naught, is no minor thing at all, but a mortal sin. Stated here in the negative, "Thou walkest not in love," this vice of not loving a brother was positively stated by John in the very next verse, thus:

Whosoever hateth his brother is a murderer; and ye know that no murderer hath eternal life abiding in him.

Paul was in complete harmony with John and all the apostles in denouncing lovelessness as a fatal offense.

Destroy not with thy meat him for whom Christ died ... shows the fruit of a loveless attitude. It will destroy a fellow child of God. Paul wrote the same to the Corinthians, thus:

For through thy knowledge he that is weak perisheth, the brother for whose take Christ died. And thus, sinning against the brethren, and wounding their conscience when it is weak, ye sin against Christ (1 Corinthians 8:11,12).

"Destroy" in this place is therefore synonymous with "perish" in the admonition to Corinth. These warnings teach emphatically that a brother's soul may be lost because of a loveless attitude on the part of some "strong" Christian, who by such lovelessness himself incurs the penalty of sinning "against Christ."