Theophylact of Ohrid

Since the apostle wrote this epistle to mature believers, some asked why he commands them to keep themselves from idols. We answer: the apostle wrote this to the entire Church, which was not entirely filled with chosen people, but among them some were also of wrong disposition. To such people he gives this commandment, fearing for their weakness.

Commentary on 1 John ↗

Oecumenius

Little children, keep yourselves from idols. Amen. "keep yourself from idols." Some have questioned: If John writes this to the perfect, why does he now command them to beware of idols? We therefore say that because he wrote to the whole Church, which was not made up of a select people, but there were also some among them who were less affected. Therefore, he commands all these, looking at their slippery nature.

Commentary on 1 John ↗

Bede

Little children, keep yourselves from idols. You who have known the true God, in whom you have eternal life, keep yourselves from the doctrines of heretics, which lead to eternal death, because, like those who make idols in place of God, they change the glory of the incorruptible God into the likeness of corruptible things with perverse teachings (Rom. I). Keep yourselves from love of money, which is the service of idols. Be careful not to prefer any worldly allurements over the love of the Creator. …

Commentary on the Catholic Epistles ↗