Thesis and antithesis. Any proposition creates in itself a negation of itself. Theism is the proposition of the existence of deities, hence atheism is its negation.
In a way, atheism is the antithesis of all religious beliefs. Just as the ideas of theism revolves around the existence of a deity (or deities), atheism address these issues around the absence of a supreme being.
Morality:
Christianity believes in moral absolutism. (God's word)
Atheist beliefs are split between moral rationalism and moral relativism. (Themselves antitheses of each other)
Science:
Christianity adopts the creationism.
Atheism follow the scientific method.
Love:
Christianity places love of its deity before all else.
Atheism believe that man's obligation is to his fellow man. (Mostly humanism, but no limited to such)
Justice:
Christianity believes in absolute and unchanging law. (God's word is law)
For atheism, laws are made by humans for humans, they can and should be changed in accordance and to support the advancement of human society.
Order:
Christianity believes in strict hierarchial order. (Divine right to rule being one of the core tenants of Christian nations for a good part of the 10th to 19th century)
Atheists beliefs in order is very varied. (As an atheist myself, I believe in meritocracy)
Life:
Christianity believes in an afterlife. And Christian instutions have long abused this belief. (Indulgences for those in the purgatory, excommunication, etc.)
Most atheists do not believe in an afterlife. I believe that this give us cause to live the life that we have to its fullest. (I don't know if other atheists share this belief)
Reality:
Christianity believes that all reality is created in 6 days and can be summed up in a single book.
Atheism believes that the above stated belief is asinine.
