One of basis of Christaintity is the Trinity which is a mystery. Also we proclaim the mystery of Faith during the Mass. Mystery implies hidden knowledge. Whether that knowledge can be gained by rational thought is a “mystery”

since we can’t know what we don’t know. It is implied that it is outside rational thought.
Leaving aside the basic question of God’s existence (ie. a “first cause”), the reality is that any “faith” we have in a Trinity, Christ etc. (ie. the Christian “faith”) depends on the testimony of others for a start. If we didn’t have the apostolic record or the Bible, we wouldn’t even begin to guess at a Trinity, Christ, the role of Mary etc.
So what we call “faith” depends in the first place on the hardwon experience of preceding generations. None of us develop “faith” in a complete vacuum.
I had the peculiar expeience of my first “double whammy” around Christmas 1983, which took place at Forest Glen Caravan Park, just south of Nambour in SE Queensland - in a specific place, at a specific time. The story is that I was helping out in a Scripture Union Beach Mission as a new Christian. I wasn’t in a good frame of mind, and I remember thinking to myself “How do I know this (Christian belief) is true?” And in that frame of mind, when the camp leader read out the words, “… a man after my own heart…” from one of the books of Samuel (referrring to David), this “double whammy” suddenly hit me - like a breath going through you in waves from head to foot.
I nearly fell off the chair, I got such a shock. And this was in broad daylight, at around 3pm in the afternoon.
I next looked around in wide eyed amazement to see what the others were making of it. But of course they weren’t taking the least bit of notice, but were just sitting there listening to the camp leader. The reason simply was that it hadn’t happened to them - the experience was hidden, and given only to me on that occasion. I had two more incidentally, both times back in my resident Presbyterian Church of the day, both times highlighting words my old pastor was saying.
However it was given in a Christian context - the leader was reading from the Bible, referring to one of the Old Testament heroes, within the context of a prophetic book.
Hence my quite reasonable assumption was that the Being who hit me with the “double whammy” was the Christian God or one of His agents eg. an angel. Without that background, had the same thing occurred in another context eg. Moslem, Jewish or Hindu, Buddhist, or even agnostic, what would I make of it?
What my previous training told me of course. So my interpretation of faith wasn’t just based on some sort of blind belief - it depended on the legacy of others, and quite a long time ago as it turns out. David and Samuel lived about 3000 years ago, but God used their history to give me a message of encouragement in Christmas 1983.