Dallas Willard in "The Spirit of the Disciplines", defines them as:
“Any activity within our power that we engage to enable us to do what we cannot do by direct effort…They are designed to help us withdraw from total dependence on the merely human or natural…and to depend also on the ultimate reality, which is God and his kingdom.”I Tim 4:7 says "Discipline yourself for the purpose of godliness" (NASB). (Or in the NIV: "Train yourself to be godly.") The word used for discipline is the same greek word from which we get the word "gymnasium", and there is a clear analogy between spiritual 'exercise' and physical 'exercise'. Verse 8 (NIV) goes on "For physical training is of some value, but godliness has value for all things, holding promise for both the present life and the life to come." (Donald S. Whitney does an excellent job of discussing the purpose of spiritual disciplines in his book "Spiritual Disciplines for the Christian Life.")
Practice of the disciplines themselves, for the sake of discipline or in our own power, do not make us godly. Only God can do that, but when we do these things in an attitude of prayer and humility, asking and expecting God to transforms our lives, a wonderful thing happens... He does! Practice of the disciplines are not an end to themselves, but are an ongoing daily choice, in which we bring ourselves to a place where the grace of God can act within and upon us.
Prayer, fasting. solitude, worship, bible reading - you've heard of many examples of spiritual disciplines. There are many others that we might not think of, yet some have been practiced for centuries. Humility, service, solitude, secrecy, stewardship and others. Over the next few weeks I'll be taking a brief look at a variety of spiritual disciplines - my professors at Rockbridge Seminary recommend that lifelong practice of spiritual disciplines plays a large role in going the distance in ministry. Some other excellent resources on the subject include: Richard Foster's Celebration of Discipline, John Ortberg's "The Life You've Always Wanted", the "Spiritual Disciplines Handbook: Practices that Transform Us" by Adele Calhoun, "Sacred Pathways" by Gary Thomas, "What's Your God Language?" by Myra Perrine, and "Sacred Rhythms" by Ruth Haley Barton.