Adam Clarke on 1 Corinthians 8:2

He knoweth nothing yet, etc. - The person who acts in this rash, unfeeling way, from the general knowledge which he has of the vanity of idolatry and the liberty which the Gospel affords from Jewish rites, with all his knowledge does not know this, that though the first and greatest commandment says, Thou shalt love the Lord thy God with all thy heart, etc., yet the second is like unto it: Thou shalt love thy neighbor as thyself. He, then, that can torment his neighbour's weak or tender conscience with his food or his conduct, does not love him as himself, and therefore knows nothing as he ought to know.