Read this: Whitehead thus sees God and the world as fulfilling one another. He sees entities in the world as fluent and changing things that yearn for a permanence which only God can provide by taking them into God's self, thereafter changing God and affecting the rest of the universe throughout time. On the other hand, he sees God as permanent but as deficient in actuality and change: alone, God is merely eternally unrealized possibilities, and requires the world to actualize them. God gives creatures permanence, while the creatures give God actuality and change. Here it is worthwhile to quote Whitehead at length:

In what way did Whitehead view God as deficient?
What is the answer? (If it cannot be answered, return "unanswerable")
deficient in actuality and change