Undiscriminating a priori skepticism is hopeless and fruitless, because if there are limits to human knowledge, then they can only be found in the process of attempting to overcome them. The success of modern science, both empirical like physics and axiomatic-deductive like economics, has shown that our collective intelligence is vast.
For example, Wikipedia mentions: “Although many initially believed it was impossible that computers themselves could actually be a scientific field of study, in the late fifties it gradually became accepted among the greater academic population.”
It is different for God. For example, Smith notes that St. Thomas argued that “to know the self-subsistent being… is beyond the natural power of any created intellect.” (65) Smith objects that a necessary being is an unintelligible concept of God. But supposing for the sake of argument that that’s exactly what God is, St. Thomas’ argument seems reasonable. If God not only exists necessarily (understood as all three of imperishability, simplicity and identity of essence and existence, and logical necessity), but is also lovable essentially (as goodness), then I see no way for us in this life to know the essence of God.
If further, God is infinite, then again, Smith quotes Aquinas: “it is impossible for any created intellect to know God in an infinite degree. Hence it is impossible that it should comprehend God” (68) not only here but even in the state of glory while beholding God face to face.
(To comprehend something is to know it fully, to envelop it in thought as a whole and in every detail. If the Father is the mind of which the Holy Spirit is the ideal thought that grasps the Son as God’s real essence, then in heaven we will be thinking this divine thought in the divine language with our human minds, though without comprehending God.)
What real difference is there between the skeptic who believes that man cannot know reality as it actually is, and the Christian who declares that man cannot know ultimate reality (i.e., God) as it actually is?
How does the skeptic who bemoans the impotence of reason to comprehend existence differ from the Christian who preaches the impotence of reason to comprehend the ultimate form of existence? (130)
The skeptic differs from the Christian in being wrong, where the Christian is correct.
There are arguments in favor of the natural limits of the human intellect as regards God which cannot be used to support skepticism about the created world. Hence the analogy fails.
In short, God really is unseen, and reason cannot discern those mysteries which belong to faith, such as that God is a Trinity. If Smith thinks it can, then let him enlighten us. Otherwise I do not see the point of his chapter on skepticism.