Here's the problem: a Christian spends some time drifting away from his Lord and His Word. Apathy soon leads to active disobedience - and that Christian is suddenly in no fit condition to act effectively for God.
Here is one solution, which involves prayerfully reading through three detox chapters of the Bible.
Penitence is first. Genuine sorrow for wrong motive, direction and/or action. Plenty of Bible passages apply, but I prefer Jonah's heartfelt prayer. He knew his disaster was entirely due to his own disobedience, and His recovery could only be accomplished by God's grace.
Passion is next. An earnest longing for God's presence, power and glory. Psalm 67 clearly cries out for this. So should we, whenever we feel its loss!
Pardon is last. With Christ's death and resurrection in mind, we know that pardon is possible in John 21. With Peter's denial and subsequent restoration, we are assured that personal pardon is bestowed by the Man who calls us, walks with us and directs us.