Lent originally was established for new Christians, those who experienced a call. They were to spend 40 days and 40 nights preparing for their baptism. If at the end they still wanted to follow Jesus, then on Easter Eve they would be baptized as the sun was rising in the east, signaling the new day, the new era, inaugurated because of the Resurrection.
I am sure it had a powerful significance for them, to have prepared for their vocation as Christians the same way Jesus prepared for His vocation as the Messiah: 40 days of introspection and self-examination.
Later, the Church used the 40 days as a time of renewal for those who were already Christians; because at a certain point everyone in the empire became a Christian; everyone was baptized as infants. So the time of Lent was used as a time of renewal and recommitment to the Christian life, examining our lives in light of the One we are supposed to follow. (Mark Trotter, Collected Sermons)