D.A. Carson once wrote: “People do not drift toward holiness. Apart from grace-driven effort, people do not gravitate toward godliness, prayer, obedience .. to Scripture, faith, and delight in the Lord. We drift toward compromise and call it tolerance; we drift toward disobedience and call it freedom; we drift toward superstition and call it faith. We cherish the indiscipline of lost self-control and call it relaxation; we slouch toward prayerlessness and delude ourselves into thinking we have escaped legalism; we slide toward godlessness and convince ourselves we have been liberated.”
It takes discipline to be a disciple, because spiritual growth is intentional not automatic. If left to ourselves, we tend to move away from God and His glory. Just as our bodies atrophy without exercise and our minds weaken without challenge, so our spiritual life withers without, as Carson says, "grace-driven effort."
Jesus is committed to our spiritual growth. He is not content to allow us to wallow in spiritual immaturity. The Bible, in Ephesians 4:15 says, "...we will speak the truth in love, growing in every way more and more like Christ, who is the head of his body, the church." (NLT) Jesus loves you the way you are, but He loves you too much to leave you the way you are. He's committed to enabling you to grow spiritually so that you become more and more like Him in every way.
That's why uncommitted Christians are spiritually miserable. They go to church, but get nothing from it. They sporadically read the Scriptures for their devotion, but see no application to their daily lives. Prayers are occasional, mostly before meals, but spoken from childhood memory rather than heartfelt devotion. They have a form of godliness (basically good people), but deny the power of it. They sense something is missing, but can't quite put their finger on what it is. Often, their solution is to withdraw and put the empty feeling on the back-burner of their lives. Because it is easier to ignore the problem than to practice the discipline needed to grow spiritually.
But it takes discipline to be a disciple. The apostle Paul wrote: Don’t you realize that in a race everyone runs, but only one person gets the prize? So run to win! All athletes are disciplined in their training. They do it to win a prize that will fade away, but we do it for an eternal prize. So I run with purpose in every step. I am not just shadowboxing. I discipline my body like an athlete, training it to do what it should. Otherwise, I fear that after preaching to others I myself might be disqualified. 1 Cor 9:24-27 (NLT)
Paul had a plan for spiritual growth:
1. He knew what the goal was - Paul knew the goal of spiritual maturity (Christ-likeness) and he went for it
2. He trained himself in godliness - Paul practiced the spiritual disciplines of prayer, study, obedience and others.
3. He lived with purpose to his life - Paul's goal in life was to glorify God in everything He did.
4. He mastered his fleshly desires - Paul made his body subject to his spiritual nature. Many times I've heard it quoted (and said it myself), "The spirit is willing, but the flesh is weak" (Matt 26:41), but I'm afraid that verse often becomes the excuse for failing to discipline ourselves in godliness.
It takes discipline to be a disciple, because spiritual growth is intentional, not automatic.