God – To understand God, first you have to understand yourself just like we are made of trillions of cells, god are made up of us, including every being - living and non- living; matter i.e. solids, liquids, gases, plasma and Bose-Einstein condensates & space, we are the small but definite mirror image of him, you can understand him as natural selection who's consistent and continuous effort made us the way we are i.e. evolved to be called human with the unparalleled physical body we possess, great mind and higher level of emotions which make us different from any other entity in the world we know. We can understand it by simple example just like a surgeon is performing any tumor resection- he knows where to give incision, how to prevent bleeding and how to do the best to remove that tumor without impairing normal and working part of body, for that he is considered god or messenger of God by layman or common people, here in this case what does that doctor actually done, he used his past knowledge and experience over the patient), for which he was given a God image. I don't know it is right to call him god or not but it won't be right if we didn't acknowledge him for his talent, which saved that person's life. Here this doctor had done this operation/s many time and have master in his field, but even though he learnt something from his last surgery similarly when we read any book again and again we learn new thing every-time from it, why I am emphasizing on the fact that we learn every-time something new when we do the act again and again because Our God or Universal Being or Ultimate Spiritual-Guide is the one who is preserving us from the starting of our existence and evolving us even now to become more better and better(with guidance, mastered by himself and this guidance over us, is referred as GOD), his aim is to take us toward being perfect but what will be the outcome when you do not learn to acknowledge him or anyone for their effort for their great act.(* I am just giving you a suggestion start thanking him from now for his giving's/effort, if you feel that there is anything mystical/different in yourself for which you can be thankful, I guess that good feeling within him can transform your existence for good). I am not saying he knows all (but no one can compare him and not knowing all means 1-2 times out of 1 billion moments) as I feel he also learn from the present, that's why our evolution is not circle its spiral but I believe he knows us that much for which he is Incomparable / Unmatchable. He is guiding us from the starting, since he realized he have the duty to preserve us beside caring himself, normally we can't even take care of our-self, then how to think about others, he made us what we are, he is the only creator(who guided our creation from bacteria/ dust to the being no one can compare), preserver(who care for us and guide us even though we are not thankful to him) and destroyer(who turn us in dust again, mainly for our evolution i.e. to carry our good karma further and to subtract our bad karma from our existence but don't try to provoke any Great Being just to satisfy your ego, he have Guru of Karma standing beside him, whom he don't need but just in case, you are trying to entangle with him).
Now what is religion and spirituality?
To understand all of this, we have to understand one example which is quite simple for a learned person but can be felt by unlearned one too. This example includes functioning of a human being, as in our body - molecules combine to form cells, cells combine to form tissues, tissues combine to form organs, organs combine to form organ systems, and organ systems combine to form organisms, who we are. So basically we are made of the combination of cells, let's call each of this cell a spirit and all of this spirit in one organism that can be anyone human being or bird or fish is referred as a single unit which is here related to Supreme Being. For instance, I am saying Supreme Being is a unit, who working single-handedly to preserve our existence is the composition of all beings in any form in our existence who are referred to as spirit. So any organism (here we take human being for a better explanation) with all of its cells which is referred as the spirit is living in harmony or mutual understanding with each other just like we are in this universe. In our existence we use to hear that Spiritual God is one just like we are to each cell of our body, in short for each cell of our body we are the only prime being, it can act for or against us but it is part of me. When we get ill all of the milieu interiors readjust accordingly to get us better, similarly when any group of spirits starts doing wrong other groups of spirits in this unit i.e. Supreme being work accordingly to restore the balance and bring us back on path, that is why whenever we get deviated from our path other good or bad spirits help us to bring back in rhythm and make us balanced. So I guess you understand what SPIRITUALITY is, it is the same for every being i.e. cell - living or nonliving in the existence to Supreme being just like we are to every cell of our body. As better said by Guru Sai that SABKA MAALIK EK.
Now, what is RELIGION, as tissues combine to form organ which is different from each other functionally but originated from same thing i.e. cells under the guidance of Natural law, Similarly Religion is formed by different Higher Being can be called as Super-human/s of past time who act different functionally but originated from the same origin i.e. spirit under the guidance of Supreme Being. Religion can be recognized as the different organ in our body, every organ has its own importance and flaws but as for working of human body every organ is needed with their pros and cons, similarly, for proper working of this Society (part of Supreme Being), Every Religion is needed with its pros and cons. We can't say in our body which organ is best and which is worse as every organ have its duty/ies to perform, similarly, Religion works in society. To understand spirituality i.e. importance of each cell which is here referred to as spirit, we have to first understand the bigger object that is Organ or Religion. The pro of Religion is that we came to know of God in our small age but the con is that he wasn't the real God but it is the ladder between the gap/s which give support to our Belief.
Now, what are being Theist, Agnostic, Atheist?
To explain all of these topics, I am just expanding the reference I mentioned in Spirituality and Religion. As I related single cell (in our body) to the single spirit (in the whole universe) and we know the fact that our body is made up of trillions of cells just like our Supreme Being is made up to trillions and trillions of spirits. Out of these trillions of cells, some are those who acknowledge the fact that they are part of our Body and work according to our will (it can be sympathetic or non-sympathetic), those can be related to Theist Spirits, who believe that they are part of Supreme Being, respect them and try to work according to his will. They are like hero's in movies can have a tough life but with good ending.
Now who are Agnostic spirit, those are the cells who sometimes know and some-time don't know who they are part of us, they just feel themselves, do their work and live happily, they believe they are born to execute their work and will die when their work will over, they don't realize they are part of any bigger realm and these spirits/cells are somewhat blessed and more happy as they are destined to perform any single and simple work with they do and go away, according to me these cells/spirits are midway in hierarchy and move forward to be Theist or Atheist cells/spirits.
Move forward to Atheist spirits, these are the cells in our body, who most of the times know that they are part of us (Human body) but they deny to accept that they are less important and moreover try to compare themselves with their Human body or even kind of challenge with their existence. They believe if they weren't there, the specific body won't be able to exist. I have one example which kind of explain Atheism better, according to the story when God made Adam from dust then he asked every other spirit to bow in respect of him as he has Heart which is the unique feature for existence for which Adam is dear to God, but jinn/Iblish (who was made of fire) refused to bow as he felt he is made of superior element for which he was banished from heaven and also referred with the name like Satan (which I personally feel is not accurate because in my religion he is Shiv who was following his God and was too loyal to Him, just can't bow anyone other to his God and due to the event he made his own dynasty(i.e. AUM) which consists of Illusion/s having layer/s to Reach or Realize Real God. At last, I feel it is the will of Supreme being for Human being to make the way across Illusion/s to reach till his home i.e. Heaven). So in sort Jinn/ Iblish / Shiv explains Atheism but actually, he is no Satan just following the will of The God.