1 Corinthians 8:7

Howbeit there is not in all men that knowledge: but some, being used until now to the idol, eat as of a thing sacrificed to an idol; and their conscience being weak is defiled.

There is not in all men that knowledge ... Some facts are of a different quality from the ordinary; and, whereas the existence of an idol is no fact at all, there is the psychological fact of its existence in the MINDS OF MEN; and Paul here drew attention to that fact, so totally passed over by the "knowledge" crowd at Corinth.

The great mass of the heathen world did regard the dumb idols as the proper objects of worship, and supposed that they were inhabited by invisible spirits.[15]

Barnes declared that "Although the more intelligent heathen put no confidence in them, yet the effect of the great masses was the same as if they had had a real existence."[16]

Regarding the rationalization by which intelligent people may worship images, and the specious logic by which the historical church itself consecrated and adored them, see full discussion in my Commentary on Romans, pp. 44-45.

Their conscience being weak is defiled ... For fuller comment on the subject of "conscience," see in my Commentary on Romans, p. 469, and in my Commentary on Hebrews, pp. 198-200.

When a man violates his conscience, he assaults the central monitor of his spiritual life; and regardless of whether or not the conscience is properly instructed, the violation of it is a spiritual disaster. This is why a person who thinks a certain action is a sin may not safely take such action.

Defiled ... means polluted, sullied and damaged; and when the conscience is defiled, any true spiritual life becomes impossible.

[15] Donald S. Metz, op. cit., p. 391

[16] Albert Barnes, Notes on the New Testament (Grand Rapids, Michigan: Baker Book House, 1949), p. 141.