Geach provides a way to sidestep two hundred years of Kantian-Analytic critique of theistic arguments by saying that the arguments use the sense of “exists” that is synonymous with “life” in living things.
The Kantian critique was that there was no more intelligible content in the existent than in the merely possible, but one can’t make the same claim about the living and the dead. The Analytic critique that making existence a predicate requires making non-existence one too, and so a shepherd should go out every morning to divide his non-existent sheep from the existent ones, doesn’t make any sense when we use the sense of “exists” that is the same as “alive” in the living. Taken in this way, it’s exactly the thing one expects a shepherd to pay attention to. In fact, the only reason that shepherds exist is to pay attention to this.
Speaking in this way also makes it much easier to understand how existence is gradient in medieval theology. Things exist more or less in exactly the ways that they may be more or less alive, or have a higher or lower sort of life.