Quite a number of translators and commentators read into this verse that the example of the godly wife wins the husband to Christ. But Peter makes no mention of Jesus in these verses, nor is he saying that a godly wife has the ability to call (see John 6:44), let alone convert, an unbelieving husband. God alone retains the power to open a person's mind and give him the faith that produces spiritual salvation.
This is not to denigrate the power of a good example in the least. Our example is a large part of whether we are upholding the holiness of God's name or bearing it in vain. Our example gives evidence of our spiritual paternity, for either we will resemble Satan or we will resemble God. When we display the same characteristics as our heavenly Father, He is glorified, and those who observe our good example can see that God's way of life produces good results.
However, even the very best example will not convert another unless God is also calling him or her. Even after 3½ years of walking and preaching on earth, the perfect witness of the Son of God did not convert everyone He encountered. If a good example were all that was needed, we could expect that everyone who observed Jesus would come to Him—but that is not what happened at all! After His death, there were only about 120 disciples (or perhaps 120 families; Acts 1:15). Obviously, God did not call every person who encountered Jesus—He will call them when they are resurrected.
Clearly, the conduct of a child of God is of utmost importance, particularly in the case of one spouse being called and converted while the other is not. Yet, even if the believing spouse sets a perfect example, “chaste conduct accompanied by fear” will not win the unbelieving spouse for Christ. Instead, the “winning” or the “gaining” in I Peter 3:1 is similar to the gaining of our brother in Matthew 18:15. Just as it may be possible (through our efforts) to have a more profitable relationship with a brother who sinned against us, so it may also be possible for a godly wife to gain the heart of an unbelieving husband, so that he respects her more and begins to let go of his animosity.
This is similar to Proverbs 16:7: “When a man's ways please the LORD, He makes even his enemies to be at peace with him.” God can cause an enemy to begin looking favorably on one of His children, and thus the former foe is gained. By our efforts, though, we can only gain a person in terms of the human relationship. We cannot cause a relationship to occur between man and God—only God can initiate that.
In the same way, the winning or gaining that Paul is striving for in I Corinthians 9:19-22 is simply protecting or improving the connection he had with the people he encountered. His gaining of these people was not the same thing as converting them or of opening their minds to the reality of God. He was trying not to be unnecessarily offensive, but the scope of his behavior was entirely on the level of human interaction, not on getting people saved in a spiritual or eternal sense.