I propose that one of the very few valid answers to the question of the title, "God is ........." is "infinitely complex beyond our grasp". While we can say those words, almost every fiber of our being rebels against that idea. Historically, the idea of a single, unitary God Who defies all definition has been mankind's most revolutionary concept and has always been resisted. On a personal level, even those of us most committed to Torah constantly must fight the urge to concretize God, at least in our deepest imaginations. It's almost impossible not to.
Most of our being, as humans, is material. As such, each of us is, substantially, bounded. Even our thoughts, when approached as merely the result of many electro-chemical impulses in our brains, are thus physical and, therefore, bounded. The mere existence of something not limited with any boundaries whatsoever so insults our very being that we're incapable of grasping it (since, without boundaries, what is there to "grasp"?).
Religiously, there has always been a current which elevates the Written Torah over the Oral Torah. One is considered (at best -- bible critics don't even grant it this status) the Word of God, the other merely the words of men. Underlying this drive is the desire to embrace what appears finite: a certain number of words, a certain number of letters, a certain weight of black ink on a certain amount of parchment, while resisting the ever-growing, tending-towards-infinity Oral Torah.
Likewise, we all have a natural tendency to concretize metaphor. We want to say that A = B and nothing else. It's too challenging to our nature to consider that A = B = C, and when that chain is extended our mind shuts down. Thus, when we declare God as מלך (Melech), King, on Rosh HaShanah we imagine an old man, wrapped in ermine cloaks, crowned with gold and sitting on a luxurious throne. In doing so, we completely miss the point.
מלכות (Malchut), which does superficially translate as "Kingship", represents both the Source of All and the Receiver of All in our deeper "mystical" tradition. An ever-generating and ever-radiating source of everything there is, matter, energy and all that lies beyond that very limited spectrum. Additionally, at each moment it also receives back this infinite transmission. To be honest with you, while I can say these words I cannot claim to really understand, grasp or even imagine that reality.
Nevertheless, we're not only limited and physical beings. Rather, our materiality encloses a spark of The Infinite in its purest form, הנשמה שנתת בי טהורה היא (HaNeshama Shenatatah Be Tahara He), "The soul (Neshama) You placed within me is pure". While our Neshama is not, by any stretch of the imagination, a sensory organ and doesn't give us a "backdoor" ability to understand God in His Infinite Complexity, it does allow us to participate in His Reality through the modality of Devekut, attachment. We can draw the Infinite Light, the אור אין סוף (Ohr Eyn Sof) into our own infinite connection, thus connecting this life-giving/sustaining energy to the physical which encloses our Neshamot.
Thus, when we declare God as מלך (Melech), we're engaging in this process which gives existence itself to all creation.
We don't need to understand, grasp or even "know" God. Rather, we experience Him in His Infinite Complexity.
May we merit many years, both in this world and the next.www.rabbizeitlin.com