Hidden things may pertain to God our Lord, but that which has been revealed applies to us and our children forever. [We must therefore] keep all the words of this Torah.
The hidden things are fear and love of God, because these things are in the heart of man. The revealed things are Torah and mitzvot, which can be observed by all.
In addition, the hidden things hint at the five Strengths, represented by letters מנצפך, which are found in the spiritual entity called Supernal Mother, and, being that she is hidden and removed, they are also called hidden. The spiritual entities of Zeir Anpin (Cosmic Man, or Small Countenance) and his Female are related to the totality of all Jews, and thus can be in some way observed in the world. But the Supernal Mother pretends that she is not there, and is thus called hidden. However, there is yet a spiritual entity even more hidden than she.
There also five other Strengths in the Cosmic Woman, a spiritual image that is closer to our world, and these are thus called “revealed.”
Art: William Merritt Chase - Hide And Seek