The “finely-tuned” universe all around us with all its intricate beauty and dazzling structure is not the only source of wonder and amazement from which Muslims can find iman-boosting signs (ayat).
Have you ever sat and thought deeply about the rules of ritual purity (tahara) in Islam? Have you ever took a moment to reflect on why the prayer (salat) is the way it is in terms of the required motions and words?
All religions have rational parts and a-rational parts (and some religions have irrational parts as well). In Islam, the fact that maghrib prayer is 3 rakat is rationally inscrutable. There is no reason for that number that we can discern. Or why is wudu broken if you pass wind but not if your face gets smeared in dirt? Why were angels made of light and jinn out of fire? And so forth.
If we go through every tenet of a religion, we can divide them into the rational and the a-rational buckets, and as a matter of fact, the a-rational bucket will always be much larger for any religion you analyze.
What this means is that, if you are trying to truly evaluate a religion for its intellectual and rational merits, you would be missing out on a lot if you only focused on the bucket of tenets that are most amenable to a kind of rational, pragmatic analysis.
So then how does one scrutinize the a-rational? Well, one looks for ayat. One ponders and reflects and if Allah gives one fiqh, i.e., profound understanding, one can see how the whole deen is suffuse with the sublime will, wisdom, and beauty of the Creator.
“Allah is beautiful and loves beauty.”