"For this is the way the holy women of the past who put their hope in God used to make themselves beautiful. They were submissive to their own husbands, like Sarah, who obeyed Abraham and called him her master. You are daughters if you do what is right and do not give way to fear." NIV translation
Peter makes it clear that he is talking about Christian women by saying "who put their hope in God". He gives the example from the Old Testament of Sarah and her submission to Abraham and reminds us that she called him master. The simple fact is that she was submitting to God as master by submitting to the authority that He delegated to Abraham. Once again, we must remember that God comes first and the wife is not to follow a husband into disobeying God. The beauty that Peter refers to comes from a close relationship with God. Obedience draws a woman closer to God and because of that she actually glows and is more beautiful on the outside than ever before.
"Husbands, in the same way be considerate as you live with your wives, and treat them with respect as the weaker partner and as heirs with you of the gracious gift of life, so that nothing will hinder your prayers." NIV translation
Now, Peter turns to being holy as a husband and tells us to be considerate. That means doing what is best for her and showing her respect. He reminds us that our wives are a weaker part but they are also heirs with us in Christ and so deserve that respect. Then, he gives us a reason for treating our wives properly and that is so that our prayers will not be hindered.
"Finally, all of you, live in harmony with one another; be sympathetic, love as brothers, be compassionate and humble. Do not repay evil with evil or insult with insult, but with blessing, because to this you were called so that you may inherit a blessing." NIV translation
Now, Peter tells us how to demonstrate holiness in our other relationships. The first thing is to live in peace (do not argue with others). We, as Christians, are to simply share God's word; it is not our job to condemn or to convince. We simply share what God says and trust Him to change people's hearts. We are to put ourselves in other people's shoes and to remember that we all need the grace and mercy of God. Even when we are persecuted, we are to bless our persecutors and remember our inheritance which is eternal life. Jesus told us that we would be go through what He went through and so we are to expect evil and insult but we will also be resurrected just as He was.