When you are in the fourth jhana you can recollect your past lives and with the divine eye you can see devas and other realms. So it is not just blind faith. You can experience them here and now in this life. In DN 2, the Buddha explained the fruits of contemplative life.
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to creating a mind-made body. From this body he creates another body, endowed with form, made of the mind, complete in all its parts, not inferior in its faculties. Just as if a man were to draw a reed from its sheath. The thought would occur to him: 'This is the sheath, this is the reed. The sheath is one thing, the reed another, but the reed has been drawn out from the sheath.' Or as if a man were to draw a sword from its scabbard. The thought would occur to him: 'This is the sword, this is the scabbard. The sword is one thing, the scabbard another, but the sword has been drawn out from the scabbard.' Or as if a man were to pull a snake out from its slough. The thought would occur to him: 'This is the snake, this is the slough. The snake is one thing, the slough another, but the snake has been pulled out from the slough.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, the monk directs and inclines it to creating a mind-made body. From this body he creates another body, endowed with form, made of the mind, complete in all its parts, not inferior in its faculties.
"This, too, great king, is a fruit of the contemplative life, visible here and now, more excellent than the previous ones and more sublime.
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to the modes of supranormal powers. He wields manifold supranormal powers. Having been one he becomes many; having been many he becomes one. He appears. He vanishes. He goes unimpeded through walls, ramparts, and mountains as if through space. He dives in and out of the earth as if it were water. He walks on water without sinking as if it were dry land. Sitting cross-legged he flies through the air like a winged bird. With his hand he touches and strokes even the sun and moon, so mighty and powerful. He exercises influence with his body even as far as the Brahma worlds. Just as a skilled potter or his assistant could craft from well-prepared clay whatever kind of pottery vessel he likes, or as a skilled ivory-carver or his assistant could craft from well-prepared ivory any kind of ivory-work he likes, or as a skilled goldsmith or his assistant could craft from well-prepared gold any kind of gold article he likes; in the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to the modes of supranormal powers... He exercises influence with his body even as far as the Brahma worlds.
"This, too, great king, is a fruit of the contemplative life, visible here and now, more excellent than the previous ones and more sublime.
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the recollection of past lives (lit: previous homes). He recollects his manifold past lives, i.e., one birth, two births, three births, four, five, ten, twenty, thirty, forty, fifty, one hundred, one thousand, one hundred thousand, many aeons of cosmic contraction, many aeons of cosmic expansion, many aeons of cosmic contraction and expansion, [recollecting], 'There I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose here.' Thus he recollects his manifold past lives in their modes and details. Just as if a man were to go from his home village to another village, and then from that village to yet another village, and then from that village back to his home village. The thought would occur to him, 'I went from my home village to that village over there. There I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I went to that village over there, and there I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I came back home.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the recollection of past lives. He recollects his manifold past lives... in their modes and details.
"This, too, great king, is a fruit of the contemplative life, visible here and now, more excellent than the previous ones and more sublime.
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma: 'These beings — who were endowed with bad conduct of body, speech, and mind, who reviled the noble ones, held wrong views and undertook actions under the influence of wrong views — with the break-up of the body, after death, have re-appeared in the plane of deprivation, the bad destination, the lower realms, in hell. But these beings — who were endowed with good conduct of body, speech, and mind, who did not revile the noble ones, who held right views and undertook actions under the influence of right views — with the break-up of the body, after death, have re-appeared in the good destinations, in the heavenly world.' Thus — by means of the divine eye, purified and surpassing the human — he sees beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma. Just as if there were a tall building in the central square [of a town], and a man with good eyesight standing on top of it were to see people entering a house, leaving it, walking along the street, and sitting in the central square. The thought would occur to him, 'These people are entering a house, leaving it, walking along the streets, and sitting in the central square.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma...
"This, too, great king, is a fruit of the contemplative life, visible here and now, more excellent than the previous ones and more sublime.
The last one is about karma so it’s possible to understand karma. It is one of the fruits of contemplative life. If you don’t believe in these things then meditate and master the fourth jhana.
