A.T. Robertson Commentary Romans 14:2

"One man hath faith to eat all things: but he that is weak eateth herbs." — Romans 14:2 (ASV)

One man (ος μεν). "This one," demonstrative pronoun ος with μεν.

Hath faith (πιστευε). Like εχε πιστιν (Acts 14:9).

But he that is weak (ο δε ασθενων). One would expect ος δε (but that one) in contrast with ος μεν. Hο is demonstrative with δε sometimes, but here is probably just the article with ασθενων.

Herbs (λαχανα). From λαχανω, to dig. Hence garden herbs or vegetables. Denney feels certain that Paul has in mind a party of vegetarians in Rome.