"There is no god but man".
Sounds like an off-brand of atheism to me.
I personally agree with Gjallarhorn on this one. Its like Existential Atheism, or atheism without nihilism. it places huge emphasis on the Method of Science.
Its important to note however that the concept of the Soul is part of Thelemic ideology... so this places us apart from the majority of (materialist) Atheists who believe in nothing that cannot be objectively measured.
Another thing that is sometiemes used to distinguish us from the LHP - is that we do believe in a "higher power"
However this "higher power" is referred to as ones Holy Guardian Angel - a literary term for "the perfected version of yourself"
Thelemites hold the belief that they have a Holy Guardian Angel to whom they must endeavour to contact and communicate with. This is called Knowledge and Conversation of the HGA. Whats this means in real terms is that we strive religiously to achieve our full potential. Our "full potential" is referred to as our True Will.
So our "God" is a perfect version of OURSELVES. We answer to no higher power than our Holy Guardian Angel if and when we achieve that state of gnosis. We recognise that but for a few examples of prodical masters, [success is thy proof - Liber AL] the majority of us have incarnated through choas into matter.. been indoctrinated by circumstance, scoiety and our parental and peer programming. The Task - is to wade through all of it and find out who your truely are and why on Earth are you here?
We use the symbolism that everyone is like a star - and every star has a perfect orbit.. The current human condition and the chaos of reality means that most of us are nowhere near "on track"... fidning your path is the key objective... and it is not necessarily easy.
Thelema puts a huge emphasis on Discipline as the key to success in becoming one HGA - or to put it bluntly - the key to becoming God.
The disicpline is necessary because we recognise that Will and desire are two separate forces. Often they oppose each other. This is a battle a Thelemite faces on a daily basis. Every action should be a Willed action... and once you know your Will - it becomes glaring uncomfortable when you realise you have not acted in accordance with it.