Catechism of the Catholic Church

The first movement of the prayer of petition is asking forgiveness, like the tax collector in the parable: "God, be merciful to me a sinner!" It is a prerequisite for righteous and pure prayer. A trusting humility brings us back into the light of communion between the Father and his Son Jesus Christ and with one another, so that "we receive from him whatever we ask." Asking forgiveness is the prerequisite for both the Eucharistic liturgy and personal prayer. (2838)