Let's be honest, most people live basically for themselves. Paul argues for a different approach to life. In other words, Paul is telling us that giving ourselves to the Lord is the logical thing to do. It's logical after all Paul has been writing. In this letter, Paul has systematically explained the gospel.
People are rebellious at heart.
Yet God loves us and has made it possible for us to have a new relationship with Him through faith. We are to have faith in what God did for us. He gave Christ as a substitute for us. His death was reckoned for our sin and His righteousness and goodness was applied to our account. Christ was our representative just as Adam was originally.