"Dear children, keep yourselves from idols".
This is the concluding command of John's first epistle. On the surface of things John has not said anything about the danger of idolatry. But implicitly he has been dealing with it all throughout his letter. This idolatry is presented in two forms. The "world" is a rival god, vying for the affections of the believer. And then there is the seduction of false teaching. This too aims to lure the children of God away from their Father.
Bruce Ellis Benson, in his book Graven Ideologies, refers to the separation from God that is entailed by idolatry. The idol is not God, and therefore it has come between us and the Father.
This separation from the true and living God is because the idol has become a substitute. Like a solar eclipse, the light has been covered. We are left without sight of the Father because a substitute has caused this separation. The chilling cause of this, according to John, is the proclamation of a false Christ. "No one who denies the Son has the Father. Whoever confesses the Son has the Father also" (1 John 2:23). What is being denied of course is not the Son's existence but his true identity as the God-Man, God's own testimony concerning him.
This is how he puts it in his second epistle (2 John 9-11):
"Everyone who goes on ahead and does not abide in the teaching of Christ, does not have God. Whoever abides in the teaching has both the Father and the Son. If anyone comes to you and does not bring this teaching, do not receive him into your house or give him any greeting, for whoever greets him takes part in his wicked works".
We should never underestimate the destructive nature of heresy. Idolatry always, and inevitably, takes us away from eternal life. This truly is the agony of deceit.
Without the Son, without the Father, without hope, without life, without comfort. The affirmation of the following question from the Heidelberg Catechism is taken away:
Question 26. What do you believe when you say: "I believe in God the Father almighty, Maker of heaven and earth"?
That the eternal Father of our Lord Jesus Christ, who out of nothing created heaven and earth with all that is in them, who also upholds and governs them by his eternal counsel and providence, is for the sake of Christ his Son my God and my Father.
I trust in him so completely that I have no doubt that he will provide me with all things necessary for body and soul. Moreover, whatever evil he sends upon me in this troubled life he will turn to my good, for he is able to do it, being almighty God, and is determined to do it, being a faithful Father.