Chapter 4 addresses two issues: The first is a reflection on the transformed life. The point here is not that the "living like the Gentiles" (2) has become illegal but that, in the light of the unspeakably marvelous love and grace of God. living like that (licentiousness passions, drunkenness, revels, carousing and lawless idolatry) has become irrelevant, dare I say silly. Why would we stoop to petty and insignificantly transient pleasures when the eternal pleasures and joy of heaven have been opened to us here and now?
1 Peter goes on to suggest that since the "end of all things is near" (7) we should use the time the world has left to usher in the kingdom of the heavens and diligently work for the transformation of our lives and of the world around us. Notice that this happens through love for each other (8); practicing hospitality without complaining (9); serving one another (10); and speaking in such a way as to glorify God and extend the kingdom (11).
The second issue in 1 Peter 4 resumes the key theme of the epistle at 4:12 by returning to the discussion of "suffering as a Christian." Unlike the modern world the ancient theology understood that suffering was an inevitable part of the everyone's journey and that suffering had transformative and redemptive qualities. The world was transformed through the suffering of God's only begotten Son, our sufferings in the name of that Son help to transform the world as well. Many ancient Christian writers believed that the soul's journey through this life required suffering to temper and form and shape it for eternal glory. It is an idea that is not often discussed and preached in the modern world (at least in affluent USofA) but I think is a Biblical way of looking at our struggles that gives meaning and purpose.