Romans 14:22-23 — Hast thou faith? have it to thyself before God. Happy is he that condemneth not himself in that thing which he alloweth.
And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.
faith — liberty, as in verse 2. Faith is necessary and good, but it's not to be displayed to show superiority.
Happy is he — similar to verse 5 "assured in his own mind." Happy for not using his rightful liberty to cause a brother to stumble.
Verse 23 is a warning to the weak.