This is an excerpt from “Spiritual Disciplines for the Christian Life” by Donald S Whitney with thoughts from Van Zyl De Villiers:

The most important feature of any Spiritual Discipline is its purpose. Just as there is little value in practicing the scales on a guitar or piano apart from the purpose of playing music, so there is little value in practicing Spiritual Disciplines apart from the single purpose that unites them (see Colossians 2:20-23; 1 Timothy 4:8). That purpose is godliness. Thus we are told in 1 Timothy 4:7 to discipline ourselves “for the purpose of godliness” (nasb).

Actually, God uses three primary catalysts for changing us and conforming us to Christlikeness, but only one is largely under our control. One catalyst the Lord uses to change us is people. “Iron sharpens iron,” says Proverbs 27:17, “and one man sharpens another.” Sometimes God uses our friends to sharpen us into more Christlike living, and sometimes He uses our enemies to file away our rough, ungodly edges. Parents, children, spouses, coworkers, customers, teachers, neighbors, pastors—God changes us through these people.

Another change agent God uses in our lives is circumstances. The classic text for this is Romans 8:28: “And we know that for those who love God all things work together for good, for those who are called according to his purpose.” Financial pressures, physical conditions, even the weather are used in the hands of Divine Providence to stimulate His elect toward holiness.

Then there is the catalyst of the Spiritual Disciplines. This catalyst differs from the first two in that when He uses the Disciplines, God works primarily from the inside out. When He changes us through people and circumstances, the process works mainly from the outside in. The Spiritual Disciplines also differ from the other two methods of change in that God grants us a greater measure of choice regarding involvement with the Disciplines. We often have
little choice regarding the people and circumstances God brings into our lives, but we can decide, for example, whether we will read the Bible or fast today.

So on the one hand, we recognize that even the most iron-will led self-discipline by itself will not make us more holy; instead, it may make us more like the Pharisees. Growth in holiness is a gift from God (see John 17:17; 1 Thessalonians 5:23; Hebrews 2:11). On the other hand, that doesn’t mean that we’re to do nothing to pursue godliness, just living the life we want until and unless God decides to make us holy. What we are to do is discipline ourselves for the purpose of godliness, practicing the God-given Spiritual Disciplines as a means of receiving His grace and growing in Christlikeness.