The human person: with his openness to truth and beauty, his sense of moral goodness, his freedom and the voice of his conscience, with his longings for the infinite and for happiness, man questions himself about God's existence. In all this he discerns signs of his spiritual soul. The soul, the "seed of eternity we bear in ourselves, irreducible to the merely material", can have its origin only in God.
Source: Catechism of the Catholic Church (Vatican.va)