Based on the variable liturgical calendar, today is Saturday of the Third Week of Lent. Based on the non-variable solar calendar, today is the Commemoration of Saint Patrick, bishop. He is remembered because he introduced Christianity to Ireland. Indeed, the prayer recited at the end of Morning Prayer and the Office of Readings says:
God our Father, you sent Saint Patrick to preach your glory to the people of Ireland. By the help of his prayers, may all Christians proclaim your love to all men. Grant this through our Lord Jesus Christ, your Son, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.
This prayer may be used only in Morning Prayer and in the Office of Readings. Commemorative prayers are not recited in any of the daytime prayers. Evening Prayer on Saturday does not belong to Saturday: it belongs to Sunday. Its technical name is Evening Prayer I for Sunday. Evening Prayer II for Sunday is what is recited in the evening on Sunday. The same principle applies to other significant days: the liturgical day actually begins on the preceding evening. No saint is commemorated on Sundays unless it is a solemnity. Commemorating saints is optional as it is.