Originally, in places where Pascha was celebrated on a Sunday, the Paschal feast followed a fast of up to two days.  In the third century, this fast was lengthened to six days.  Eventually, the fast became attached to, or overlapped, another fast of forty days, in imitation of Christ's fasting in the wilderness.  The forty-day fast was especially important for converts to the faith who were preparing for baptism, and for those guilty of "notorious sins" who were being restored to the Christian assembly.  In the western church the forty days of Lent extend from Ash Wednesday through Holy Saturday (at the end of which is the Great Vigil), omitting Sundays.  (Sundays are "in Lent" and not "of Lent" -- this allows us to celebrate the Eucharistic Feast during a period otherwise reserved for fasting.)  Today Lent has reacquired its significance as the final preparation of adult candidates for baptism.  Joining with them, all Christians are invited "to the observance of a holy Lent, by self-examination and repentance; by prayer, fasting, and self-denial; and by reading and meditating on God's holy Word.”  (These words come from the Ash Wednesday liturgy in our Book of Common Prayer.)  It is important to note, however, that the principal purpose of fasting is not to "punish" the body, but to realign oneself to God.  The prophets speak of "fasting" from selfishness and greed, and from words and deeds that hurt or oppress others.  "Self-denial" doesn't necessarily mean giving up chocolate (for example) - it can, and perhaps should, mean giving up making assumptions about people or re-posting tweets without verifying them (for example).