Zubiri's argument for God parallels the phenomenological "method of immanence," not the one condemned as modernism , but the corrected version offered by Maurice Blondel. Like Blondel, Zubiri starts from the fact of being immersed in reality to achieve both a recognition of the need for the transcendent and a simultaneous admission that reason cannot penetrate into the transcendent, thus establishing the need for revelation. In Zubiri's version of the argument, the "power of the real," the fact of being immersed in reality, produces what Zubiri calls the "problem of God." Zubiri's argument has some advantages over Blondel's in being metaphysical/ontological rather than dialectical, thus avoiding potential pitfalls associated with Neoplatonic reduction to an infinite number of "structures of mediation," in which respect Blondel veers toward being too Hegelian despite consciously rejecting Hegel's conclusions. For more about the perils of Neoplatonic dialecticism in Christian thought, see the introduction to J.P. Farrell's translation of Photios (but be wary of his treatment of St. Cyril, which doesn't adequately distinguish between hypostatic and energetic procession).
In Zubiri's account, the recognition of reality as dar de si, giving of itself, and its power to impose itself upon ("religate") sentient intelligences leads to the concept of an "absolutely absolute reality" from which the dynamis of reality stems. The absolutely absolute reality does not stand in relation to other reality; rather, all of reality stands in relation to the absolutely absolute reality. One may immediately see the relationship between this concept and the hyperousios ousias of the Fathers, and indeed, Zubiri's absolutely absolute reality is utterly incomprehensible, infinite in its fecundity, and entirely beyond being. Thus, the immanent argument that Zubiri presents is similar in its import to the telelogical argument of the Cappadocians based on the sheer complexity and order of creation, but it reaches the same conclusion by a different route, starting as it does from the basic fact of immersion in reality (religation) and reasoning from the nature of reality itself to the unlimited and unknowable absolutely absolute reality. Notably, Zubiri reasons from the concept of divinity itself (absolutely absolute reality) to God as person, since the original definition of the "problem of God" that pointed to divinity was itself the personal relationship of the man with reality. Thus, rather than demonstrating sheer divinity in the abstract in terms of being (as Anselm or Thomas Aquinas purport to do in their ontological arguments), Zubiri affirms both divinity and personhood in God, a significant step beyond what could be achieved by the "ontological" method.
And with that cursory introduction, I will now defer to the greater expertise of Brad Elliott Stone in his analysis of Zubiri and the problem of God.
