God has masked His own nature because there is too much ecstasy. At the time when He again realizes His own nature, He feels that the ecstasy was already there.

Pillars of Creation

 (from "Self Realization In Kashmir Shaivism" by Swami Lakshman Joo"):

eṣa devo'nayā devyā nityaṁ krīḍārasotsukaḥ|

vicitrānsṛṣṭisaṁhārānvidhatte yugapadvibhuḥ ||6||

The supreme Lord Siva, who is all-pervasive and fond of playing and falling,  together with the Energy of His own nature simultaneously brings about the varieties of creation and destruction. [Bodhapanchadashika 6]

Swami Lakshman Joo: This supreme Lord Siva, who is all pervasive along with the energy of his own nature, creates varieties of creation and destruction. He creates everything in this world: birds bugs, whatever is possible and whatever is not possible. And He doesn’t create it in succession. He creates it simultaneously. The purpose is to discover that God's Consciousness also exists in all creation. 

What is the Energy of His own nature? Universal Existence, the universal cycle of the Universe. With this universal cycle, Lord Siva is fond of playing and also falling. Take the example of young boy. It may happen that when this young boy becomes too excited he begins to jump about wildly and may bump his head. In the same way God has masked His own nature because there is too much ecstasy. He wants to disconnect that ecstasy, but that ecstasy, in reality cannot be disconnected at all. The Lord knows that but still for His own amusement, He temporarily disconnects it. Then at the time when he again realizes His own nature, He feels that the ecstasy was already there.