Deuteronomy 29:29 The secret things belong unto the Lord our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law.

With God the revelation of a secret thing is done with purpose. Here in the Old Testament, it is meant to help them obey the law. It is but a help. This is important.

That is the OT, what is the New Testament equivalent of this passage?

Romans 16:25-26 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,  But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:

So here in the NT the revelation purpose of the hidden thing is obedience of faith. OT obey the law, NT obey faith. Here once again, it is meant to help, and is not responsible for performance. We on the other hand have the opportunity to get help in obedience.

Allow me for a moment to speak to the inquisitive nature of mankind, we do love a mystery. We love a good puzzle don’t we? We love discovery. We love to be in the know. We love to understand, discover, and uncover things before anyone else. We were given the power to reason.

What is the power of reasoning without revelation with purpose? It is called vanity.

Ecclesiastes 1:14 I have seen all the works that are done under the sun; and, behold, all is vanity and vexation of spirit.

Vexation of spirit here means frustrating the spirit. The spirit will reveal the mysteries of God with purpose but using the power of reasoning in this way frustrates the purposes of God.

That is the true nature of vanity.