‘But sanctify in your hearts Christ as Lord, being ready always to give answer to every man who asks you a reason concerning the hope that is in you, yet with meekness and fear,'
So they are rather to ‘set Christ apart in their hearts as holy', (or ‘acknowledge Him in their hearts as holy'), and as their ‘Lord' (in contrast with the false ‘lords' of idolatry), and be ready to give an answer to anyone who asked them for the reason for the hope that was in them. He is enjoining them to become sure of their own position, and of Who possesses them, (compare here 1 Peter 2:4-5), and to then be able to put it into words, so that they could set it reasonably before others, in order both to appease their masters, and in order to win others to Christ.
‘Set Christ as Lord apart in your hearts as holy.' Christ as their Lord was to have full and total possession of them and the central place in their lives. People often had places in their houses set apart for the gods, such as a ‘god-shelf'. But the Christian looked on himself as the sanctuary of Christ his Lord. He was a ‘God-shelf' on which Christ abode. He was the Temple of the Holy Spirit (1 Peter 2:4-9; compare 1 Corinthians 3:16; 1Co 6:19; 2 Corinthians 6:16-18; Ephesians 2:20-22).
In these days when the occult, which had so long been suppressed in the ‘Christian' West, is again raising its head, we once again need to be able to refute it in positive terms by pointing to Christ to whom the whole spiritual world has been brought into subjection. The occult is a further attempt of evil spirits to break into the world and possess human beings. And we overcome them because Greater is He Who is in us, than he who is in the world (1 John 4:4). It is as a result of the coming of the Spirit and the arrival of the Kingly Rule of God that they can be defeated (Matthew 12:28). Thus we do it by having Christ set apart as holy in our hearts. But we do not approach the problem lightly. We do it in humbleness and the fear of God (compare Jude 1:9).
It is important to recognise that idolatry and the occult are not just human folly, they are also connected with evil spirits. ‘The things which they sacrifice, they sacrifice to demons (evil spirits)' (1 Corinthians 10:20). This had long been recognised (Leviticus 17:7; Deuteronomy 32:17). Thus Peter was very much aware of what these churches were facing in areas where idolatry abounded. And he wanted them to stand firm in Christ.
There is an echo in 1 Peter 3:14-15 of Isaiah 8:12-13, ‘nor fear you their fear, nor be afraid, sanctify the Lord of hosts Himself and let Him be your fear'. But the cause of their fear was different from that in mind in Isaiah. On the other hand, in both cases the Lord was the antidote to their fear.