Walsh is offering philosophically what Joseph Ratzinger has offered at the core of his "Introduction to Christianity," namely Trinitarian Person is the total meaning of reality - i.e., being. He offered the same in his keynote address at the Synod of 2008 as Benedict XVI: the Word of God, the Person of Christ, is the meaning of reality and all realism. In the "Introduction..." Ratzinger offered that the "Father" is not the Father and then engenders the Son, but is the action of engendering the Son. Hence, what we mean by being in our immanent experience through senses and abstraction is not fully real. Only Person as the act of transcending Self is real. All of this beggars language because to say anything is to say this or that. But the Person of the Father - or the Son - or the Spirit - is neither this nor that, but "for" the Other. At one point below, Walsh will say: "Being must be discovered, not as the alternative, but as the possibility of the person. It is within the horizon of the person that the whole movement of existence can be contained. There is no other model available. Immanence and transcendence are fragmentary aspects of what the person alone makes whole. There is no ontology of the person becasue the person is the encompassing ontology. The only reason that our philosophical discourse has not descended into sheer chaos is that we have integrated in person what we could not integrate in thought. It is what we have known all along yet never found the way to admit. Persons stand outside of being. Is that not the presupposition of the Parmenidean pronouncement of the Is? Could he have declared being if he was not apart from it?" Later Walsh says: "Our purpose here is to sketch that recentering of reality within the person. Instead of seeing the person within reality, now we must attempt to find reality within the person. This is not suggest that we embrace a radically subjective perspective, for subjectivity is only a possibility for person who are not reducible to it. Persons can behold their own subjectivity, demonstrating that they are as much objective about themselves. The categoris simply do no apply." (See below).
When I first "saw" that "Father" in the Trinity is not "Father" as individual, and that He is "only" "merely" "simply" the action of engendering the Son, and that the "to be" of Father is action/process, I immediately thought of St. Thomas's Esse which was so uniquely his insight as the prius of all metaphysics. Thomas saw esse as the action of all actions and perfection of all perfections (S. Th. 1,3,1 ad 3), in relation to which everything else is a potency, and which tends to infinite perfection unless limited by such a potency. What else could esse be except person? And yet, since it is action as the relation of engendering, as person, it could be irreducibly different if it was an opposing action such as glorifying and obeying, which would be the person of the Son? And I began to think further when St. Thomas said that all that God gives in creating is esse in an infinity of stages of limitation whereby it becomes "this" and "that."
Notice that all this is said in a deductive mode. I think that what you will see in this "introduction" by David Walsh is a positive, experiential mode, not inherently theological as my deductivity, because he is trying to see into what is there of myself in the living out of political life.