(The following is from DAVID GUZIK COMMENTARY ON THE BIBLE)
Do not let your adornment be merely outward; arranging the hair, wearing gold, or putting on fine apparel; rather let it be the hidden person of the heart, with the incorruptible beauty of a gentle and quiet spirit, which is very precious in the sight of God.
a. Do not let your adornment be merely outward: Peter does forbid all adornment. But for the godly woman, outward adornment is always in moderation, and her emphasis is always on inward adornment.
b. Rather let it be the hidden person of the heart: Real beauty comes from the hidden person of the heart. It isn’t something you wear or primp for. It is something you are.
i. The real question is “What do you depend on to make yourself beautiful?” Peter’s point is not that any of these are forbidden, but that they should not be a woman’s adornment, her source of beauty.
c. The incorruptible beauty of a gentle and quiet spirit: The inner beauty of a godly woman is incorruptible. This means that it does not decay or get worse with age. Instead, incorruptible beauty only gets better with age, and is of so much more value that the beauty that comes from the hair, jewelry, or clothing.
d. A gentle and quiet spirit, which is very precious in the sight of God: Peter describes the character of true beauty - a gentle and quiet spirit. These character traits are not promoted for women by our culture, they are very precious in the sight of God.