As a practical response to our union with Christ, we are to yield our lives to Him as willing and submitted servants. It is an act of the will based on the knowledge of what Jesus Christ has done for us. This is why the first half of chapter six is so important. Here in the second half, Paul reminds his readers that a man is a slave to the one he commits himself to obey. To be a slave of something is to become an instrument in serving its interests. Who will I serve?
All of us serve something, it is just a matter of who or what. It is fundamental to human design. The key to a full life is slavery to the right Master. God’s purpose in saving sinners from their sin is not to give them freedom to do as they please or to live for themselves. His purpose is to give them the freedom to do as He pleases, which is to live righteously. God delivers us from slavery to sin for the sole purpose of becoming slaves to righteousness.