Similarities (and differences) of Atheism and Monotheism

For Monotheism, I will substitute Christianity, for it is the one prevalent pure form of monotheism that exists today. Atheism has many branches, but we will leave it at that for our purposes here.
Obviously, atheism and Christianity are mutually exclusive at the core. The cores respectively being 'all that exists is because of chance' and 'all that exists is because of God'. They both claim the source of the universe is eternal, and quite frankly, neither can prove either of their positions on this by means of the physical (or metaphysical). Both make claims to a distinguished superior characteristic. Atheism claims that the physical is the only way to understand the universe and to get answers about why we are here. Christianity claims that the spiritual is the ultimate route to discovering truth. I suppose it is unavoidable that each must ultimately be in direct defiance to the claims of the other.

Well, firstly I will address the issue of the claims that each makes about their distinguishing characteristic.

Today, Christianity makes the claim to be superior in the spiritual, but now many attempts are also made to reconcile it with science (the physical). With the current train of thought (and some beliefs and doctrines) that most Christians have adopted, this is simply not possible. It is interesting to note that atheists only shy away from any attempt to reconcile their beliefs with spirituality (inevitably, there will always be some who try to mix and match, but we are only concerned with strict atheists). What is interesting to observe in my opinion, is that for the most part both push away the other's strong suit, if I may use the card analogy. This, in my humble opinion, is where the heart of the matter lies. This is where I believe, if we are to seek for The Truth, we will find it.

--Truth emerges more readily from error than from confusion - Sir Francis Bacon