Many people look down on institutions or organizations that openly claim to keep secrets. Christians have been one of the harshest critics about this and baselessly claim Masonic secrets are kept for nefarious reasons. Yet even Christianity veils truths in their scripture and their teachings. Just about every esoteric and/or occult group, practice veiling their deepest truths in symbolism and allegory. Even nature hides Truths in plain sight.
Below are some quotes on the subject, one even coming from the bible.
Masonry, like all the religions, all the Mysteries, Hermeticism and Alchemy, conceals its secrets from all except the adepts and sages, or the elect, and uses false explanations and misinterpretations of its symbols to mislead those who deserve only to be misled; to conceal the Truth, which it calls Light, from them, and to draw them away from it. Truth is not for those who are unworthy or unable to receive it, or would pervert it.
Albert Pike
Do not give what is holy to dogs; and do not cast your pearls before swine, or they will trample them underfoot and turn and mow you.
Matt 7:6
There are a few reasons this is done and it’s not done for any nefarious reasons. Though, obviously a corrupt institution can do it for nefarious reasons.
One of the main reasons this is done is to prevent people from perverting the truth for their own gain. I can use the mainstream accepted “Truth” about Lucifer, from the Bible, as an example. The veiled truth is that Lucifer (as stated in the Bible, he is the Light Bringer) is to be thought of more as a force, not an existing personified demon. Understanding Lucifer as a force means that as an individual, seeing evil in their heart, has to take responsibility for that evil. Because it is a force that stems from them and that they partake in. If the uninitiated, profane, and/or unworthy find out this truth they would pervert it. They would rather think of Lucifer as a personified demon, as something separate from them, so that they can avoid all responsibility for that evil. “It’s not me, it’s the devil, it’s his fault!”
People would rather deny the torture of understanding their baser yearnings in self deceit. The more the actual truth is pushed on certain individuals the more they push back. Self deceit turns into denialism and a whole new way of seeing the world. These people build a new a better truth for themselves, at the detriment to the world around them, so it’s better to veil these deeper truths from the profane.
Another main reason the truth is veiled is because truth is actually a very subjective thing. “Truth is the aim of belief” and we all have different beliefs and aims.
Truth is the property of being in accord with fact or reality. In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs, propositions, and declarative sentences.
Wikipedia: Truth
Just telling an individual the Truth doesn’t work, they have to find the Truth for themselves. So you veil the Truth in such a way that it leads people on a journey to discover it for themselves, in their own way.
Without this method people will never understand the Truth on their own. This is the main reason Masons hide their Truths in symbolism and allegory. This is the philosophy of a Freemason, to attempt to lift the veil of reality into the deeper Truths that lay hidden in plain sight.