Romans 14:23

And--rather, "But" he that doubteth is damned--On the word "damnation," see on Rom 13:2. if he eat, because he eateth not of faith--On the meaning of "faith" here, see on Rom 14:22. for whatsoever is not of faith is sin--a maxim of unspeakable importance in the Christian life. Note, (1) Some points in Christianity are unessential to Christian fellowship; so that though one may be in error upon them, he is not on that account to be excluded either from the communion of the Church or from the full confidence of those who have more light. This distinction between essential and non-essential truths is denied by some who affect more than ordinary zeal for the honor and truth of God. But they must settle the question with our apostle. (2) Acceptance with God is the only proper criterion of right to Christian fellowship. Whom God receives, men cannot lawfully reject (Rom 14:3-4). (3) As there is much self-pleasing in setting up narrow standards of Christian fellowship, so one of the best preservatives against the temptation to do this will be found in the continual remembrance that CHRIST is the one Object for whom all Christians live, and to whom all Christians die; this will be such a living and exalted bond of union between the strong and the weak as will overshadow all their lesser differences and gradually absorb them (Rom 14:7-9).

— Jamieson-Fausset-Brown Commentary (public domain)