Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will. Romans 12:2 NIV
The theologian and writer C.S. Lewis in his book The Screwtape Letters, chronicles the exchange between a senior demon, Screwtape, and his nephew, a junior demon in training Wormwood. Each letter from Screwtape contains reproaches and new suggestions on how to turn the target human, the Patient (man), away from the Enemy (God). I won't ruin the ending, but I encourage you to read for yourself.
While Lewis' story is a work of fiction, it is a true tale. The more we grow closer to God, the harder Satan fights. One of the most accessible weapons Satan has is what Paul talks about in this verse, conformity–going along with the sins of this world. But when we receive Christ into our hearts, a transformation takes place. We can no longer follow the world, lapsing back into sin, and also claim to be a child of God: we are either Christian or not.
Does this mean we will never be tempted and stumble when we accept Christ? Oh, I wish that were true! But, as in the letters, the forces of darkness are always there to pick at our scabs. Though God has forgiven us, our memories of our weaknesses remain, and that's where Satan prods. He's not smart, but he is tenacious.
Though we are tested, we have hope through Jesus Christ. While we are tempted by sin, we have another memory, not of who we were, but of what God has done. So, while we will always remain sinners in recovery, thanks to the transforming power of the Holy Spirit, we can come to know his "good, pleasing and perfect will."
Thank you, God, for the transformation in our lives. We have become a new creation reconciled with you. Help us be obedient to the Holy Spirit, rejecting the temptations we face this day. In Jesus' name, we pray. Amen.