From the Summa:
“The divine processions can be derived only from the actions which remain within the agent. In a nature which is intellectual, and in the divine nature these actions are two, the acts of intelligence and of will. . . . It follows that no other procession is possible in God but the procession of the Word, and of Love.”
Given that God the Father is both personal and supremely good, it is proper to think of Him as loving a person from eternity. This other person is the Son, and the love between them is the Holy Spirit. This Augustinian analogy may be imperfect, but it may help us as we attempt to visualize the divine Trinity.
“Preach the Gospel at all times; and if necessary, use words.” -St. Francis of Assisi