What does 1 Peter 3:4 mean?

This verse concludes a sentence begun in verse 3. This is part of a passage where Peter gives instructions specifically to Christian wives, in verses 1–6. Peter writes that Christian wives should not seek their "adornment" or "beauty" or identity in how they dress or wear their hair. This is in no way meant as a ban on braiding or jewelry. Rather, it's a warning about using external things in an attempt to find true beauty.

Here, Peter describes what Christian wives should focus on, instead. God's will for them is to "adorn" or "beautify" themselves from the inside out. They should let the "hidden person of the heart" show up visibly in their life. That inner self should be characterized by the beauty of a gentle and quiet spirit. That's a beauty that won't fade with age, a beauty that is of great value to God.

In the context of this chapter, cultivating that inner beauty of a gentle and quiet spirit—and allowing her husband to see it in her—is one way a Christian woman will "win" him to faith in Christ.