This is not a density of knowing

[Illamasqua]

So blindly believing any metaphysical material that has its core in the unknown, is dogmatic by its very nature, and however many correspondences are found in the various materials does not account to knowledge.

Correct.

However, your assumption precludes the very real possibility that some entities may simply know things (albeit in semi-to-very distorted fashion) by virtue of the fact that they hail from a density of awarenes higher than 3rd, and that this knowledge may then surface or otherwise percolate into said entity's conscious mind complex at some point or another, whether by spontaneous bleedthrough, momentary parting of the veil, traumatic experience, out-of-body experience, direct ET contact, or a plethora of other means.  

That aside, you do bring up a very important point: the dichotomy between knowing and believing. Belief implies an uncertainty, a suspicion, a vacillation. Knowledge, does not.

Knowledge (Latin: scientia; Greek: gnosis), by its very nature, can only be attained by direct, empirical, self-validating experience. Keyword is worth reiterating here: experience. Anything unverified by experience falls into the wayside of rumor, hearsay, opinion, speculation, superstition and/or confabulation.

This may seem astoundingly discouraging; however, the exact opposite effect is intended here: there should be nothing more uplifting, motivating and invigorating than this very realization. Hence, two of the most important aphorisms (which, despite being about 2 thousand years old, most spiritually-inclined people still don't seem to fully comprehend—let alone put into practice):

1. scientia est potentia (Latin: knowledge is power)

2. γνῶθι σεαυτόν (gnothi seauton; Greek: know thyself)

Has anyone ever learned how to swim or ride a bicycle by just reading a book or online article, watching some YouTube video, or just hearing someone talk about it? No.

Sure, one may learn about the experiences of others (very often subjectively [mis]interpreted by their various cultural, religious or intellectual/emotional backgarounds, biases and limitations), and these experiences may no doubt prove to be quite valuable, especially in terms of their more general or broader implications (e.g. if millions of people are reporting "alien abduction" experiences all across the world, no matter how cognitively dissonant their perceptions may be—same goes for the mounting evidence of OBEs & NDEs accounts—then perhaps it would be logical to conclude something worthy of investigation is going on here, no?).

One can at best be be inspired by the experiences of others. However, an over-reliance on the external (that which is outside one's experiential nexus) will invariably lead to stupefaction of mind sooner or later (in effect, one ends up becoming a pop-science junkie, a conspiracy junkie, a lecture/workshop junkie, or some other type of "junkie" sitting behind a computer screen all day long), as the fact still remains: the entity in question does not know how to swim or ride the bicycle—all it does is read and watch and hear and talk about it.

(And curiously enough, those who talk the most are often those who know the least.)

Therefore: experience is of paramount importance here.

So how does one even begin to experience anything, you say?

One seeks.

And the most valuable seeking is that of the heart of the self. And the greatest aid/tool in this seeking is that of meditation (this cannot be and can never be over-emphasized enough no matter how many times it is repeated ad nauseam). Once that is done (and not without a certain degree of purity of intention and sincere, honest, genuine application), one has opened the gate to experiences of the "paranormal," "metaphysical" and "otherworldy" kind.

One then does not read or hear about it, one knows—not by words, but by direct, empirical, self-validating experience.

Therefore: look up not to self-appointed "online gurus," self-proclaimed "starseeds," and other assorted "spiritual guides" of equally variegated flavour to bequeath unto you their lofty pearls of wisdom—no, look into the mirror.

---

And no, 3rd density (whether pre- or post-veil) is emphatically not the density of understanding (one does not understand how physics really work, what gravity or electromagnetism is really all about, one does not even understand astronomy, or biology for that matter; no, there's so much one does not understand—you believe you do, but you really do not). These understandings are properly of 4th density.

But guess what? 4th density gotta begin somewhere.