John Calvin Commentary 1 Peter 5:8

"Be sober, be watchful: your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour," — 1 Peter 5:8 (ASV)

Be sober. This explanation extends further: since we are at war with a most fierce and powerful enemy, we must be strenuous in resisting him. But he uses a twofold metaphor: that they should be sober and exercise watchfulness. Overindulgence produces sloth and sleep; in the same way, those who indulge in earthly cares and pleasures think of nothing else, being overcome by spiritual lethargy.

We now understand what the Apostle's meaning is. We must, he says, wage war in this world; and he reminds us that we are dealing with no common enemy, but one who, like a lion, runs here and there, ready to devour. From this, he concludes that we must watch carefully. Paul motivates us with the same argument in Ephesians 6, where he says that we have a contest not with flesh and blood, but with spiritual wickedness, etc. But we too often turn peace into sloth, and consequently the enemy then circumvents and overwhelms us; for, as if placed beyond the reach of danger, we indulge ourselves according to the will of the flesh.

He compares the devil to a lion, as if to say that he is a savage wild beast. He says that he goes round to devour, in order to rouse us to wariness. He calls him the adversary of the godly, so that they may know that they worship God and profess faith in Christ on the condition that they will have continual war with the devil, for he does not spare the members, since he himself fights against the Head.