Finally then, brethren, we urge and exhort in the Lord Jesus that you should abound more and more, just as you received from us how you ought to walk and to please God; for you know what commandments we gave you through the Lord Jesus. For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God; that no one should take advantage of and defraud his brother in this matter, because the Lord is the avenger of all such, as we also forewarned you and testified. For God did not call us to uncleanness, but in holiness. Therefore he who rejects this does not reject man, but God, who has also given us His Holy Spirit.
My parents never left us kids alone without some kind of instruction. If they took a day trip somewhere, we knew that we did not simply have a free day to ourselves in the house. There would be work for us to do, some kind of chores to complete. At a minimum, we had to follow their instructions regarding what we could and could not do while they were gone. Being the youngest, I had to listen to everyone. My older brother and sister would be left in charge, and I would be told to obey them. Of course, I often did not obey them because I did not feel they had any authority over me. I saw no problem with my disobeying my brother or sister even though they were only parroting what my parents had said. I did not see it as disobeying my parents in some way.
In this passage, Paul is the big brother giving the instructions he received from the Lord. He makes a point of saying this, and I can only assume the reason is that his audience did not understand the weight of his words and what their disobedience actually meant. There was a reason beyond simple obedience to what Paul was teaching. The point of this teaching was that God wanted their sanctification. In adhering to what Paul taught and keeping themselves from impurity, they would be agreeing to and cooperating with this sanctification plan. To disobey this instruction would be to fight against the sanctification God was trying to complete in them. When we sin, when we disobey God, we fall out of agreement with him and his plan for our sanctification.
God assigns shepherds to watch over his sheep for a reason. The spiritual leadership He gives us here on Earth is part of his structure of spiritual headship. As we obey our teachers and leaders, those who speak and instruct the truth of God, we obey God. As we disobey them, we disobey God, but it is not just about following the rules. This is about the necessary transformation that He wishes to effect in his Church. Whether we yield to sin or to self-denial in obedience shows whether we agree with God’s work of sanctification in us. Father, bring us in agreement with your plan of sanctification, and help us remain obedient to those You have ordained to lead us.