"'Did God have a mother?'" Children, when told that God made the heavens and the earth, innocently ask whether God had a mother. This deceptively simple question has stumped the elders of the church and embarrassed the finest theologians, precipitating some of the thorniest theological debates over the centuries. All the great religions have elaborate mythologies surrounding the divine act of Creation, but none of them adequately confronts the logical paradoxes inherent in the question that even children ask."

I wonder why the author of the quote put God having a mother in the past participle.

I think that the answer to this question is simple, I find it interesting to read that church fathers and theologians would be stumped by it, if that is true. Why would God have anything, as he (using language that we mere humans can make sense of here - calling God a "he" as though he were a person) has been self-sufficient from the beginning. This is the greatness of God, and why followers of the Abrahamic God strive to obtain the Holy Spirit - so that we may too might become immortal in our self-sustainability.