Confessing that we are sinners, we fast as a sign of grief and repentance for sin. This is the purpose of all our Lenten penance: to assist us in being genuinely sorry for our sins and to offer some reparation in union with Our Lord who offered His life in sacrifice to take away our sins.
We are bound specifically to fast from food on Ash Wednesday and Good Friday by having only one full meal. The fast used to be very much more strict throughout Lent, but we are now permitted to choose some act of penance such as giving up something that we normally enjoy.
St Augustine said: “Fasting cleanses the soul, raises the mind, subjects one’s flesh to the spirit, renders the heart contrite and humble, scatters the clouds of concupiscence, quenches the fire of lust, kindles the true light of chastity.” Fasting also enlightens our soul and makes us more open to the divine so that the mind rises more easily to heavenly things. It is a strong support to our practice of prayer.
We should never become vain about our fasting, and in accord with the whole purpose of Lent, we must accompany fasting with rejection of sin and the celebration of the sacrament of Penance.