The answer
The Bible meant the harmful knowledge that troubles man's mind.
There is information you gain, that might bring on you spiritual fights and lusts, which later on you regret having known it.
There are readings and knowledge that might bring doubts and affect one's faith. Other information, may affect one's good feelings toward others, or may lead one to judge them, and in all that, one might regret having known it.
Therefore, a person should have control of what to know and what to read.
Not every thing should be known to every one. Some things may open one's eyes on things not in his favour to know at a certain age or in certain psychological status, or before spiritual or mental maturity.
Of this and other similar cases the sage said "for in much wisdom is much grief".
As for the rest of the good and useful knowledge the doors of learning are wide open for all.
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Thrice-Blessed Pope Shenouda III of Blessed Memory