There’s a lot more to mind than rational thought. The intellect is very important, but its range of operation is restricted to the known and knowable. The worldview afforded by the rational mind is incomplete, but according to that worldview the incompleteness is just due to a lack of information. Rationality takes for granted that given enough time, resources and data, everything could potentially be intellectually accounted for.
But there is an aspect of mind that takes a very different and complementary perspective. It’s not concerned with knowing. You could say that it’s the mind of not-knowing, in that it contemplates reality without breaking it up into knowable chunks, instead leaving it whole and unprocessed. The perspective that this function of mind yields can’t be formulated as a compendium of facts without losing the truth of it.
These aspects of mind are constantly working seamlessly together to create our experience. We can look at them separately, as I’ve just done, but that’s an artificial exercise. It’s easy to be aware of the workings of the rational aspect of mind, because it is overtly conscious. Since it deals in the knowable, its conclusions can be discussed and explained and justified. The rational mind starts to look like the sole custodian of the “real”.
The other aspect of mind, the holistic function, is every bit as vital, but it operates quietly, at a less conscious level. Without it, though, consciousness wouldn’t even be possible. Its perspective informs, stabilizes and balances a healthy mental life (which I assume is what you mean by “mental strength”). Leave it out of consideration by denying all but the rational, and an unease may settle in. That unease is the persistent clamor of the holistic aspect for recognition. It feels like a nagging intuition that we’re overlooking something important.
I have my issues with the Bible, which is why I set it aside long ago, but I do recognize that it speaks to this nagging intuition. It says, in effect, “that ‘something missing’ is God”, and then purports to inform us about God. This vaguely scratches that itch to bring this holistic mind out of the closet. I happen to think that this approach can only go so far in scratching the itch; at least that was my experience.