OK. So apart from the obvious lack of a belief in a god, are religious theists and atheists always that different?
Atheists see no such thing as 'sin' in the concept of it being against a god. They do however accept a concept of “sin” against humanity, therefore a kind of objective morality still exists.
We (atheists) can accept that we can always be better and we want and do work to improve ourselves (similar to acknowledgement of being sinful or falling short of a god’s standard).
We believe there is no “holy spirit” to help us improve, but still recognise that we do still need help! We find it again, in humanity. There is also no real concept of “perfection” as there is (nor has been) a being completely “without sin”.
Another difference is the way the world is viewed perhaps? A theist may see the world as being less than it was meant to be; God’s perfect creation ruined by sin. An atheist however views the world in what could be seen as a more positive light; The world was never meant to be perfect! Even though there’s defiantly plenty of crap, it is amazing and inspiring to realise how much goodness there is in this world, without a god needing to make it.
A third major part is the concept of an afterlife. An atheist finds little comfort in the thought of everlasting life or paradise if it comes with the understanding that other human beings could be going to hell. Surely it is a much nicer thought that all humans simply rot after this lifetime and are never to exist again than it is to think that even one individual, no matter how “evil”, would exist in eternal torment.
Of course what we want or like the sound of doesn’t dictate what is true! Neither do the things we may be afraid of, but it is confusing to me when the idea of heaven is presented as a positive part of religion.

Humanists love humanity as a whole in the same way theists may love a god. By doing this they happen to also be doing what most god’s apparently want anyway, “love thy neighbour” etc.
Prayer is another key difference I can think of. No words are spoken to a personified god but the idea (at least in christianity) of “praying continuously” still applies in a way. This sort of prayer is continually asking/wanting to do what God would want and hoping for the ability/opportunity to carry it out. Of course the “god” of the Humanistic atheist doesn't really exist, but the same thoughts that would have been directed at him are still there.
A big question may be; OK so if there is no God then why? Why be “good”? Why do these things? - Well if there is no God then love still exists! Love is a choice. You don’t “fall in love” with your God, you choose to love him, and continue to choose to love and follow him every day. In the same way you can choose to love humanity.
It is easy to love a god that is "perfect". Humans however are not. Also if there is a god then you apparently have to love him or else! With humanity it is entirely optional with no heavenly reward or punishment. Surely this could be seen as a greater love?
A big question may be; OK so if there is no God then why? Why be “good”? Why do these things? - Well if there is no God then love still exists! Love is a choice. You don’t “fall in love” with your God, you choose to love him, and continue to choose to love and follow him every day. In the same way you can choose to love humanity.
It is easy to love a god that is "perfect". Humans however are not. Also if there is a god then you apparently have to love him or else! With humanity it is entirely optional with no heavenly reward or punishment. Surely this could be seen as a greater love?
The English language slaughters the word "love". A four letter word that can be attributed to a thousand different scenarios with important differences! But that is a rant for another time...
So what are the rewards for loving your fellow human if there is no god? - Well, happiness!
So what are the rewards for loving your fellow human if there is no god? - Well, happiness!
Why does this way of life bring happiness? Does it come from God? - Perhaps. Although I would argue that evolutionary psychology has a role to play there, but that is also an extended topic for another time.
"Evolutionary psychology tells us that we have instinctual prejudices against people different from us. One of the tasks of a civilizing culture, then, is to educate and work against this inherent tribalism – to look beyond the differences in order to identify the similarities; to recognize, share, and rejoice in those things that unite us rather than divide us." - Michael Werner
Perhaps the most important part of our beliefs, whatever they may be, is why we hold them.
Fear is not a good reason to hold a belief, at least not on it's own. Although many atheists may accuse theists of holding their beliefs purely due to this motivating force (theists may even accuse atheists of the same), it is however unlikely that this is the case.
Love is an excellent reason to hold a belief. Ask any religious individual why they follow Jesus or Islam or any other religious teachings and 'fear' is unlikely to be amongst their vocabulary. Human nature is generally to want to be good, to be better. It isn't hard to recognise that we aren't perfect! Whether we are meant to be or not may be open for debate, but the simple fact is that the majority of us want to love. And to be loved.
Though not a christian, I like Dawkins and other atheists still hold up the "Golden rule", "Do to others as you would have done to you". (Just because the bible may contain a similar message does not make it true)
Some readers may be thinking, "Hang on! - Evidence! Reason! Logic! - THESE are excellent reasons to believe something! Why have they not been mentioned?"
Of course science is a beautiful and creative tool we humans use to understand the world as it really is! But we are not all "scientists". We do however all feel emotion.
Emotions are powerful. Emotions inspire change. Emotions make us human (though animals also feel emotion). Love may be a choice, but it can also be an emotion. The desire for it certainly is! True love connects us, it transverses divides, overcomes fear, crosses cultures and brings us together.
"Remember your humanity and forget the rest"