It is the “heart” that harbours the real self. The wives Peter is here addressing (1 Peter 3:1) had been born again
(1 Peter 1:3) and so were changed by the Holy Spirit (John 3:5–8) to treasure “a living hope” centring on an imperishable “inheritance” (1 Peter 1:3–4). Though this treasure is today “kept in heaven for you” (1 Peter 1:4), it is already treasured in the heart (Matthew 6:21). From this reborn, heaven-focused heart emanates a lifestyle that reveals what your real priorities are. These priorities are “hidden” inasmuch as the eye does not immediately see them (in contrast to externals as braided hair, golden jewellery, or clothing). Yet what is hidden has a way of revealing itself.
4 but let your adorning be the hidden person of the heart with the imperishable beauty of a gentle and quiet spirit, which in God’s sight is very precious.