1 John 5:21 - Matthew Poole's English Annotations on the Holy Bible

i.e. From those idolatrous communions with the Gentiles in their worship and festivals in their temples, which these pseudo-christians had latitude enough for, as appears by the apostle St. Paul's discourses, 1 Corinthians 8:1-13 10:14 (especially if any danger did urge); wherein, instead of that communion with the Father and the Son, which \1 John 1:3\ he was inviting them to, they should have fellowship with devils, as that other apostle tells his Corinthians, 1 Corinthians 10:20,21. And he might also have reference to the peculiar idolatries, which this sort of men are noted to have been guilty of towards their great sect master.