Peter does not say explicitly what sins he is thinking of. But the reference in 1 Peter 4:2 to “human passions” (with examples in 1 Peter 4:3) and the instruction to “cease from sin” (1 Peter 4:1) indicates that the apostle is reckoning with the fact that God’s born-again children will stumble into precisely these very sins they used to embrace and that their contacts still embrace. Temptations are real! Not only the (perceived) strong need to be earnestly loved but also those brothers and sisters who fall. Sincere love will cover many such sins.
8 Above all, keep loving one another earnestly, since love covers a multitude of sins.