Attempting to prove the existence of God through natural reason has been looked upon by some believers like theologian Karl Barth and philosopher Soren Kierkegaard as demeaning to the faith or incontestably impossible. Still, some of the greatest minds in the Christian tradition have not shied from the challenge. For following on the affirmative answer to an sit ensues an unending number of equally important questions as to quid sit. The nature of God as one comes to envision it is very much related to the kinds of behaviors that tend to follow from it. An absolute God of rules and retribution motivates attitudes and actions quite different from a relational deity whose primary attributes are love and mercy. Furthermore, arguments as to God's existence and nature can serve apologetic purposes in discussions with those seeking motives for belief or dispelling doubts among the wavering.

Kainz impressive list of publications on Hegel, ethics, phenomenology, and human nature attests to the expertise he brings to his enquiry. Although limited in length, the book covers an extensive ground of concerns from within theology, philosophy and contemporary science in the development of its analyses. While the faith instinct is the predominant concern of the study, and faith is an obvious internal condition of the believing subject, only passing mention is made of the first classical medieval assertion for the existence of God, Anselm's ontological argument. Kainz appears too quick to dismiss Anselm's position by interpreting Aquinas holding that ‘the idea of “real existence” doesn't necessarily produce real existence’ as his final word. He has not taken into account the entire context of Aquinas’ reply to objection 2 as being within the confines of the limited understanding of an inadequately prepared intellect, as well as what Thomas maintains in the response, that ‘God exists’ is a self-evidently known claim, though only to the cognoscenti. Were it self-evidently known ad omnes no one could maintain that God did not exist anymore than one could declare the part to be equal to or greater than the whole.

There is another aspect of this question that bears on Kainz's intent, the reply to the first objection. For John Damascene the existence of God is placed within the mind of all. Thomas qualifies this by noting that while true it is so in only a general and confused way. What Kainz sets out to examine in greater depth are the various ways in which this initially vague and imperfect knowledge is found in the human soul and made clearer and more specific in a wider area of human interests and in divers ways than was available to the medieval theologians. He will also make the case that ‘the concept of faith in the New Testament seems to go well beyond both traditional Catholic and Protestant understandings’ of its meaning (the concern of the fourth chapter), and that it ‘is an instinctive endowment in all rational beings.’

The first three chapters are concerned with the existence of God, the problem of evil (natural and moral) and the characteristics of God. The first chapter examines arguments as to God's existence from cosmological, biological, and scientific perspectives including the place that evolution and chance (as seemingly operative in natural selection) have impacted the discussion. The third chapter looks at the characteristics of God as these have been understood through unaided natural reason as well as described in both the Old and New Testaments.

Faith, the faith instinct, and the proper and improper objects of faith constitute the subject matter of the next three chapters, the books central concern. Faith is distinguished from belief as commonly understood–a halfway state between ignorance and knowledge. As well, Kainz takes into account the difference between natural faith and faith in God. An example of the former would be faith in oneself, the kind usually manifested in the aspirations one has as to one's future accomplishments or in progress or in science. Faith in God goes far beyond this for it is not limited to any specific object or range of experiences but extends to all possibilities. Also discussed is the objective aspects of faith on creed and doctrines and the subjective aspect of the human will's unconditional commitment to Christ focusing on grace and forgiveness–emphasizes that are at the root of Catholic and Orthodox disagreements with mainstream Protestant traditions since the sixteenth century. Irrespective of which approach dominates in the soul of a given believer, Kainz is concerned to ascertain the internal source or impetus or instinctive basis making the faith response possible. Even more to his point is realizing in a fuller sense the commonality of transcending connections between the natural and the supernatural as it applies to and is manifested collectively by humanity.

How one defines instinct about the faith inclination is critical. Perhaps the word drive or inner need would be more applicable. Irrespective of which may be the more apt term, a comparison is made between the faith instinct and sensitivity to the natural moral law that resides in human beings. The value of a moral order which all, save a minority of moral defectives, come to appreciate serves, mutatis mutandis, as an example of what Kainz is seeking to discern as to how human beings are ‘hard wired’ to faith in God. Alongside the idea of a higher power or Supreme Being, there also exists in the soul the desire for complete happiness and its corollary, unending life, which cannot be satisfied by any of the external objects or situations in this world. These may be vaguely or clearly perceived and articulated, both as to the internal condition itself and the external environmental factors or objects which activate them and bring them to fruition – points taken up on the sixth chapter.

In chapter seven, the ramifications implicit in what has been concluded about the faith instinct in areas such as the salvation of the non-evangelized, both before and after the ages of revelation, are treated. Beginning with the loosely described ultimate end God intended in establishing a chosen people that would be a light for other nations, to the clearer articulation of the soteriology explicit in the New Testament, Kainz takes up the problem of salvation for the unbaptized or those who have not heard the Gospel message. Are the prescriptions of Scripture that seem to exclude salvation to those who have not received the initiation rites and the decree ‘outside the church, no salvation’ to be taken as absolute and allowing of no exception?

Kainz does not take that extreme position and defends his stance by considering the minimum requisite content for saving faith as developed by medieval scholars and contemporary theologian Max Seckler. Furthermore, he takes into account how the God of Christian revelation makes available the resources needed to those who seek him but are prevented from finding him through the Gospel message, who live in circumstances inhibiting access to it through coercion (e.g., Red China, North Korea) or have substituted a deficient prophetic tradition in its place (e.g., Mormonism, Islam). Instances of those who were able to overcome such obstacles by seemingly miraculous interventions are presented as examples available as correctives in some circumstances, but it needs to be noted these are given by God according to conditions which we can only guess at and should not be presumed upon in all cases. But what about those not blessed with this kind of divine mediation?

In the section dealing with obediential potency, Kainz probes more deeply into the ontic conditions of the faith response which is true of all, to which they have direct access and need not depend upon the miraculous. The views of Karl Rahner and Henri de Lubac are taken into account. While they may disagree as to exactly how grace is involved in the production of implicit faith they concur that all humans have a natural orientation to it and the ecumenical implications, according to Seckler, that are entailed in holding such a position are also brought into the discussion.

In the section dealing with alternative or substitute materials for faith, the doxology and moral practices enjoined on the believer are considered. These are the external truths and values to which the internal condition of faith responds, and they have a social dimension within which they need to be affirmed and practiced. But how does one tell among diverse creeds and practices which is more in line with the divine will and which are less so, or not at all? Kainz explores the place of tradition within any religious context as well as its relation to the wider world of those who do not subscribe to its central tenets as a way of answering the question. How internally consistent are the creeds and codes among critical believers and how plausible and appealing are their exercise likely to be taken by those outside the fold? A more direct way that God is seen as offering evidence of his preference is through public miracles (e.g., Lourdes, Medjugorje, Fatima and Zeitun) although these can be problematic as to their interpretation. Hundreds of thousands of Muslims witnessed the apparition of the Blessed Mother atop the dome of a Coptic Christian Church near Cairo (widely reported in the Egyptian media) which sadly resulted in few conversions and seen by most Muslims as an affirmation of the truth of Islam, not Christianity.

In the final section, Kainz attempts to place us in the mind of atheists with respect to their difficulties in accepting the truths not only of theism generally (there are so many contrary versions of it) but of Christianity specifically. The triune nature of God, the Incarnation, the redemptive sufferings of Jesus and other basics of the Christian creed are notions that boggle the mind of many a rationally thinking person. Nor does the present day scandal of Christian disunity do anything but add more fuel to the fire of doubt. Kainz concludes however, that if humanity is ‘hardwired’ to consider ultimate causes for the totality of existence, atheism can well be more of a ‘fairy tale for adults’ than is its theistic alternative.