Why Is He Hiding Himself

מלכותך מלכות כל עולמים וממשלתך בכל דור ודור

This world is filled with G-d's presence EVERYWHERE. However, in order for His kingship to be recognized through our free will, He must hide Himself. He hid himself through the creation of the world for the very creation of matter hides His existence.  He also hides Himself through time for He is above time.

מלכותך מלכות כל העולמים-  Your kingdom is complete through the עולמות the worlds you created which veil [העלם Means hidden] your presence.

וממשלתך בכל דור ודור - Your rulership is also hidden through the creation of time  - generation after generation.

עי' מי מרום תהילים ליתר העמקה.

לזכות כל תועי בינה שסרו מדרך השם