How many of you could go out right now today and run (not walk, run) every step of a marathon? I'll put it a second way. How many of you could go out right now and run (not walk) every step of a marathon today if you tried really, really hard? Not many more.
Now my guess is a lot of us, maybe most of us, could eventually run a marathon if we did one thing, and that is to train. What does it mean to train? To train means I arrange my life around those activities that enable me to do what I cannot now do by direct effort. We tend to overestimate what we can do by trying really hard and underestimate what we can do by training. As a general rule (this is just wisdom about the human condition), transformation involves training, not just trying.
This is true in athletics. It's true of music or intellectual life. It is no less true of character formation or spiritual life. This is why Paul says, "...train yourself to godliness." This is why Jesus says, "The student is not above the teacher, but everyone who is fully trained will be like their teacher." So now the spiritual disciplines are practices or activities that train us or give us power to live in the goodness of the kingdom.
I know. Words like discipline or training are awful words. They just sound really unattractive. Who wants to do that? This is really key. Spiritual disciplines are not necessarily unpleasant. What discipline you need to practice depends on for what you're training. If you're training for a race, you will need to practice running. If you were training for a pie-eating contest, what would you need to do? You would need to practice eating a lot of pie. If you eat a lot of pie every day, a year from now, you'll be able to eat much more pie than you could today by trying really hard.