A.T. Robertson Commentary 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." — 1 Corinthians 8:7 (ASV)

Howbeit in all men there is not that knowledge (αλλ' ουκ εν πασιν η γνωσις). The knowledge (η γνωσις) of which Paul is speaking. Knowledge has to overcome inheritance and environment, prejudice, fear, and many other hindrances.

Being used until now to the idol (τη συνηθεια εως αρτ του ειδωλου). Old word συνηθεια from συνηθης (συν, ηθος), accustomed to, like Latin consuetudo, intimacy. In N.T. only here and Joh 18:39; 1 Corinthians 11:16. It is the force of habit that still grips them when they eat such meat. They eat it "as an idol sacrifice" (ως ειδωλοθυτον), though they no longer believe in idols. The idol-taint clings in their minds to this meat.

Being weak (ασθενης ουσα). "It is defiled, not by the partaking of polluted food, for food cannot pollute (Mr 7:18f.; Luke 11:41), but by the doing of something which the unenlightened conscience does not allow" (Robertson and Plummer). For this great word συνειδησις (conscientia, knowing together, conscience) see on Ac 23:1. It is important in Paul's Epistles, Peter's First Epistle, and Hebrews. Even if unenlightened, one must act according to his conscience, a sensitive gauge to one's spiritual condition. Knowledge breaks down as a guide with the weak or unenlightened conscience. For ασθενης, weak (lack of strength) see on Mt 26:41.

Defiled (μολυνετα). Old word μολυνω, to stain, pollute, rare in N.T. (1 Timothy 3:9; Revelation 3:4).