The Holy Trinity is the central mystery of the Catholic faith: one God in three divine Persons — the Father, the Son (Jesus Christ), and the Holy Spirit. Each Person is fully God, yet there is only one God, not three. The Father is not the Son, the Son is not the Spirit, and the Spirit is not the Father, but all three are the one eternal God. This is not a contradiction but a mystery that exceeds human understanding. The Trinity was revealed progressively through Scripture: the Father in the Old Testament, the Son in the Incarnation, and the Holy Spirit at Pentecost. St. Patrick famously used the shamrock (three leaves, one plant) to explain this mystery. The Feast of the Holy Trinity is celebrated the Sunday after Pentecost.