Jamieson, Fausset and Brown on Romans 14:20

20. For--"For the sake of"

meat destroy not the work of God--(See on Ro 14:15). The apostle sees in whatever tends to violate a brother's conscience the incipient destruction of God's work (for every converted man is such)--on the same principle as "he that hateth his brother is a murderer" (1Jo 3:15).

All things indeed are pure--"clean"; the ritual distinctions being at an end.

but it is evil to that man--there is criminality in the man

who eateth with offence--that is, so as to stumble a weak brother.