In Chapter 6, Landsburg makes a number of claims, some of them false, and others rather good.
He begins by describing his Orthodox Jewish friend Misha proclaiming every day that "I believe with perfect faith in the coming of the Messiah, and though he may tarry, nevertheless I believe." Landsburg objects in reply: "I believe with perfect faith that the square root of two is an irrational number, but I have never felt an ongoing need to announce that conviction to the Universe. That's why I suspect that Misha is a liar." The reason is that Misha must be brainwashing himself: "the 'beliefs' I echo are those I might want to believe, or those I'm trying to talk myself into, or those that I'm trying on for size. But when I pass the threshold to actual belief, I stop reviewing the matter." (55-6)
But this confuses reason and faith as sources of belief. Thus, I believe that Christ is Lord with "perfect" faith, while Landsburg believes that "the square root of two is an irrational number" not with perfect faith but with perfect reason.
What is faith? It's an assent of the intellect to the revealed knowledge of God. Specifically, "to faith those things in themselves belong, the sight of which we shall enjoy in eternal life, and by which we are brought to eternal life." (ST, II-II, 1, 8) There are secret things that are of God that humans cannot discover by reason alone but that can only be known through divine revelation. Thus, the Bible relates: "Jesus spoke to them only in parables, to fulfill what had been said through the prophet: 'I will open my mouth in parables, I will announce what has lain hidden from the foundation [of the world].'" (Mt 13:34-35) Of course, Christianity itself is not an esoteric religion at all; all its gems are hidden in plain sight.
St. Thomas writes that faith stands midway between science and opinion. This becomes clear if we compare the relative strengths of the influences that impel a person to come to believe. A scientific demonstration of a conclusion will move the mind to accept the conclusion as true inexorably. Scientific evidence is seen either by sensation or reflection and hence has intrinsic power to convince. For example, seeing chlorine produced from salt is sufficient to persuade anybody of the correctness of the chemical reaction
2NaCl + 2H2O → Cl2 + H2 + 2NaOH.
On the other hand, faith requires an act of choice to give in to God-given disposition to believe and to accept the unseen knowledge revealed to one by God -- knowledge that cannot be obtained by scientific investigation. One can go either way, but when the assent is given, the falsity of the propositions opposite to those that are the object of faith is not in doubt, precisely as is the case with scientific demonstrations.
By contrast, opinion is changeable and readily accepts the possibility of the opposite and so can at any time be swayed by new arguments: "the intellect assents to something, not through being sufficiently moved to this assent by its proper object, but through an act of choice, whereby it turns voluntarily to one side rather than to the other: and if this be accompanied by doubt or fear of the opposite side, there will be opinion, while, if there be certainty and no fear of the other side, there will be faith." (ST, II-II, 1, 4)
Here is the clincher: this choice must be made anew every day, and therefore the confession of faith must be recited every day as a sign of one's preference.
I find no need to keep declaring that God exists, either; I know it in the same way in which Landsburg knows the properties of the square root of two. I do not "announce to the Universe" that "there is a God, and He is simple, eternal, perfectly happy, all-knowing," and so on. I already have excellent reasons for believing all this, having proved it to my satisfaction through philosophy. I may still invoke these facts in my prayer, anyway, insofar as "things which can be proved by demonstration are reckoned among the articles of faith, not because they are believed simply by all, but because they are a necessary presupposition to matters of faith, so that those who do not known them by demonstration must know them first of all by faith." (ST, II-II, 1, 5, reply 3) Note, however, that the Nicene creed is only about faith-based knowledge, e.g., "We believe in... the Father, the Almighty, Maker of all that is, seen and unseen. We believe in one Lord, Jesus Christ, the only Son of God..." That God is a Trinity is a revealed truth.
Again, "the existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected," says St. Thomas (ST, I, 2, 2, reply 1). This natural foundation for faith requires perfect intellectual consistency and coherence of natural theology. Any flaw in our metaphysics, concept of God, meaning of life, and so on can cause the entire structure of nature + grace to collapse. An intelligent person already suspicious of faith who perceives mistakes in our reasoning is unlikely to believe.
The choice to believe is neither irrational nor a type of violent self-brainwashing. It is aided from below by lack of contradictions in the purely rational conception of God and related matters, by how well the faith builds on natural knowledge, and by personal virtue that does not cloud the intellect through sin and hypocrisy; and from above by divine grace which creates a lyrical enchantment with the articles of faith. Faith and science are similar in the sense that assenting to true beliefs and rejecting false beliefs, as a rule, leads to happiness, while the opposite actions lead to misery.
Now science is amenable to new evidence. But then so is faith. Like science, faith improves with time and always has, both "in the number of articles believed explicitly, since to those who lived in later times some were known explicitly which were not known explicitly by those who lived before them" (ST, II-II, 1, 7); and in our understanding of them.
Finally, faith is not a purely speculative subject but is also a master plan of the life-long project of saving oneself, of earning heaven. Reciting the confession is a way to re-affirm one's commitment against every temptation and evil. We can see that Misha, though a Jew and not a Christian, is acting 100% reasonably and honestly.