Today is Ash Wednesday, when Christians around the world have ashes put on their foreheads to represent mourning and repentance. This is the first day of Lent, when we follow in the footsteps of Jesus as he prepared for his public ministry by spending forty days in the desert wrestling with Satan. It is a time for us to clean house spiritually, to examine our lives for sin, repent, and draw closer to God.
There are three Lenten disciplines which the Great Tradition has taught us to keep during the next 46 days (six are Sundays where in the West there is still feasting): prayer, fasting, and almsgiving.
All Christians are supposed to do all three of these things throughout their lives. But in Lent we are to do each in a special or extra way.
In the Eastern Orthodox churches, Christians go without meat and dairy products throughout Lent, but in the West Catholic Christians fast meat on Fridays and have only one large meal a day (with two smaller ones). Anglicans fast in a variety of ways. Many give up alcohol and sweets, and all food one day a week.
The purpose of fasting is to recognize in a deeper way our dependence on God. Feeling weak and tired, which often comes from fasting, can do that. We realize in a more tangible way how much we need God.