2 Peter 3:17

‘You therefore, beloved, knowing these things beforehand, beware (or ‘guard yourselves') lest, being carried away with the error of the wicked (or ‘the lawless'), you fall from your own steadfastness.'

With a final ‘beloved' Peter makes his final appeal before his death (2 Peter 1:13). He points out that now they have been forewarned of what the situation is, and what it will be (compare Acts 20:29). Thus they are to ‘guard themselves', because they are under God's protection (1 Peter 1:4), lest they be carried away by the erroneous teaching and behaviour of ‘lawless men' (compare 2 Peter 2:7). They are to be firm in their own steadfastness so that they do not fall. Compare Paul's similar vivid call to steadfastness in Ephesians 6:10. It is a call to put on the armour of God.