Faith. Trust. Not "beliefs", not any number of beliefs, but trust.
Where do you put your trust? Faith in the Tooth Fairy won't do it.
There's something here to be known, like you know 2 + 2 or like you know the ground under your feet or the person who raised you.
And you can trust it. You can't always trust your ideas about it; these come from it and point to it, but they aren't the same.
Ideas about it can be collected, classified, marketed, used to scare people out of their savings or to let them imagine that having the ideas makes them special.
You can test people on the ideas, separate the A's from the F's, lead them around by the notions, make them do tricks, face death or kill each other.
You can't do that with What-It-Am. You can use the words; there's no way to patent them; but "There's something here to be known."
If you yearn for that, and all you're getting from your own teachers are the same old ideas that haven't done it for you yet--and may not have led them anywhere closer--Well of course you'll look in other religions. Sometimes you'll see what's been buried in plain sight among the relicts of your home tradition, whether or not you ever come to recognize it there. But that is not what Jesus is complaining about in this latest passage. These people know all the words, and if they'd found it anywhere, they would recognize it in him. But they don't, and they aren't even looking.
Can you tell if someone else knows it? Once you know what it looks like in yourself, it can be perfectly obvious when someone else is talking about the same "thing". What if he's fooling you?--What if he's only learned some good words and is just running them through his inner word processor? Well, then, someday he will connect the words with their meaning; and truth meanwhile can still come to you through his words. God is a source of truth and understanding, not a charm against surprises or a recipe for infallibility.
But where do "beliefs" come into this? They are not the same as "knowledge", but they do matter; they can lead us closer to knowledge or further away. It may or may not be worth asking: "How and why do they end up affecting what actually happens to us?"--but that's for another post.
Beliefs by definition are what we think we know, so we aren't given an operational means of making the distinction... unless we simply find God directly.
That's my definition of Quakerism--not that any number of men can render themselves foolproof, but that God is available to all. Be still, ask, expect to be answered.