Despite the undeniable utility of scientific inquiry, it is largely inadequate to answer spiritual questions-questions that are arguably the most important ones we face. While science can tell me how best to reach a certain objective or what to expect from the natural world, it can't transcend the natural world to provide answers about meaning and purpose.
This observation is no indictment of science. It's just how things are. If we trace back natural laws to moments after the Big Bang, we find that they suddenly fail to hold. Laws we typically accept as fact are broken, it seems. We can no longer use our conventional tools to answer important questions. What was before the big bang? What is smaller than a quark (or insert the latest vogue subatomic particle)? What is past the edge of the universe? ... all seem out of reach. Even granting the theoretical ability to answer those specific questions, there will ALWAYS be something out of provable reach, as Gödel has gone ahead and shown. Let me say it again: on the most fundamental level, there will always be something just out of the reach of observation, measurement, and even logic.
One may choose to be satisfied with these limitations, but I'm prone to believe that there is a fully spiritual aspect to my humanity, and that addressing it may transcend those limitations. Maybe it just requires a different approach. I hunger for meaning and spiritual knowledge. How I find that spiritual information is still subject to rational processes but is not subject to all the assumptions of science (and therefore may not be subject to all its limitations).
Many are quick to point to the widely disparate conclusions drawn by those pursuing spirituality. They conclude that none of those spiritual views have any merit over the others. This is invalid. I believe that some spiritual conclusions are right, and some are wrong. Some are incomplete or inferior. And some are supernal and real. Faulting spirituality for its non-demonstrable nature shows a misunderstanding of the rules of the game, and denying that reason plays a role is equally incorrect. We ought to have respect for differing views without accepting them all as having equal merit. Some spiritual views are irrational, yes. But calling all spirituality irrational is a fallacy of generalization.
There are admittedly many perils inherent in any subjective process, but those perils can take you in opposite directions. I've met folks who interpret Mary's face on a piece of toasted cheese to be a sign from God, and although I can't rule that out, I agree with those who note such random "signs" will happen with certain regularity over time based on probability alone. On the other hand, categorically dismissing spirituality as the result of misinterpretation of coincidence in all cases is unjustified. A rational person will recognize that the existence of such misinterpretation and coincidence does not rule out the discovery of genuine spiritual information in some cases. That is, there are both real and mistaken spiritual experiences, and one's discovery of the existence of the latter shouldn't lead one to fallaciously generalize all spiritual experiences by all people to that group.
The notion that an all-powerful Father in Heaven has created this universe and our souls for purposes that can only be partially represented to our mortal minds as "joy" and "exaltation" establishes a framework from which to understand our spiritual world. The scenario is fleshed out quite reasonably and rationally with an explanation that God's interactions with man are limited and indirect because those circumstances are necessary for development of a righteous will and maturation of a divine nature. Further, the idea that God provides information through a nuanced combination of personal revelation and authoritative messengers makes a lot of sense.
Spiritual inquiry necessarily uses reason and logic, but expands acceptable working data past what is reproducible and demonstrable. Clinical trials and retrospective analysis are key for discovering and believing what can't be overtly proven (and must therefore be based on faith). But the data turned up by such analysis can only be personally appreciated, and may therefore get a lot of scorn from those who have had a vastly different personal spiritual experience and have no context to appreciate an individual's specifics.
Spiritual truths are most immediately meaningful for what they tell us about living life abundantly, finding joy, and being filled with other divine attributes like love. Spiritual inquiry, because of its subjective nature, is often condemned for its non-reproducibility. But this non-reproducibility is expected within the context of a personal spiritual journey in which transcendental truths are available on a need-to-know-when-you're-ready basis. So, ultimately, it comes down to each individual and his or her own experience. And my experience tells me that spiritual inquiry has been extremely successful in my life in providing meaning and purpose. It has been extremely successful in making the people I admire into the people that they are. It has been extremely successful in predicting what will make me happy and help me flourish. Basically, I like spiritual inquiry because it works really well.
Index to series:
Rational faith 1: Science
Rational faith 2: Spirituality
Rational faith 3: Grand unifying theory
Rational faith 4: Creative calculus
Rational faith 5: Wrap up