From the Orthodox perspective:
For Spiritual Exercise
“Every athlete exercises self-control in all things. They do it to receive a perishable wreath, but we an imperishable …. I discipline my body and keep it under control, lest after preaching to others I myself should be disqualified” (1 Cor. 9:25, 27, ESV).
Lent is a time of year to remember that God has seen fit to make us not airy spirits but embodied human beings living in a beautiful, material world. The soul fills the body the way fire fills a lump of coal, and what the body learns, the soul absorbs as well. Spiritual disciplines such as fasting are analogous to weight-lifting equipment. One who uses them in a disciplined way will be stronger, not just when he’s lifting weights, but also for every situation he meets.
While some people think of Lent as a time to personally choose something to “give up,” the practice of the Eastern Christians, from the earliest centuries, is to observe a common fast. This is not a complete fast, but rather abstaining from meat and dairy—basically a vegan diet. Tertullian (A.D. 160-225) likened it to Daniel’s diet in the king’s court, when he abstained from meat and rich foods and grew stronger than those who feasted.
There’s something to be said for following an ancient, universal Lenten custom like this instead of choosing your own adventure. Most of us are not capable of being our own spiritual directors. We don’t have the perspective needed to choose the things that will really change us. (Deep down, we may not even want to change. I like to say, “Everyone wants to be transformed, but nobody wants to change.”) A fast like this, observed for 2,000 years by Eastern Christians in lands from Eastern Europe to Africa, India, and Alaska, is time-tested. (The Lenten vegan fast was once a Western custom too, seen by some churches still holding a “pancake dinner” just before Lent to use up the butter, milk, and eggs.)
In Lent we are one not only with the church through time, but also with those in our local church. Orthodox Lent begins with the Rite of Forgiveness, in which all church members form a circle and, one at a time, stand face-to-face with each other and ask forgiveness. This experience is profoundly healing and also preventive; I’m more likely to restrain a harsh word in July if I recall that I will have to ask this person’s forgiveness again in March.
Lenten disciplines train us like athletes, strengthening our earthly bodies and souls, healing the body of believers in our local parish, and forging union with the body of Christ throughout time. “Forgetting what lies behind” and the sins of the past, we “press on” to combat those sins that lie ahead, made stronger by our Lenten disciplines, “for the prize of the upward call of God in Christ Jesus” (Phil. 3:13-14, ESV).