Theophylact of Ohrid

Having taught us which sin is unto death and which is not unto death, he then indicates who can sin unto death, and says: one adopted by God can never be afflicted by sin, whether unto death or not unto death. For having once surrendered himself to Christ, who dwells in him through adoption, he remains untouchable by sin. …

Commentary on 1 John ↗

Oecumenius

We know that whoever is born of God does not sin, but he who has been born of God guards (τηρεῖ) himself, and the wicked one does not touch him. Having declared this, he subsequently indicates whose sin is the sin leads to death; and he says that whoever is born of God does not sin. For when he has once entrusted himself to the one dwelling in him through adoption in Christ, he remains inaccessible to sin. …

Commentary on 1 John ↗

Bede

But the generation of God preserves him, etc. The grace of Christ, by which the faithful are reborn, preserves those who are called holy according to the purpose, so that they do not commit sin leading to death; and if they err in anything due to the frailty of human condition, it protects them from being touched by the malignant enemy. Furthermore, it must be said, we remain in the generation of God as long as we do not sin; indeed, those who persevere in the generation of God cannot sin, nor be touched by the malignant. …

Commentary on the Catholic Epistles ↗