A backslidden or lukewarm Christian who is not in prayer, who is not serving the Lord, who is not reading the Bible, who is not growing in faith is no problem to the devil. After all, he has already lost that soul. He can't drag a believer into hell, but he can hope to keep them ineffective. When he sees a Christian beginning to get fired up for Christ (as was happening in me though I didn't recognize it yet), Satan doesn't like it because when said Christian gets fired up and begins to pray and live for God, he or she will make a difference for the kingdom. Guaranteed. You cannot love God and not have it spill over onto other people.
This paragraph reminds me of my own life.
I used to be a lukewarm Christian. Then I was basically dragged away from church entirely for a few years. But God intervened via the move of significant other and via a friend so I began to get fired up and pray and live for God. From then on, no amount of mocking could drag me away from Him anymore.