Christianity is defined by a belief in something -- particularly, a belief in the God of the Bible. Atheism is defined by a non-belief in something -- particularly, a non-belief in the God of the Bible.
Christians choose to be identified by that which they believe to be true. Atheists choose to be identified by that which they believe to be false.
The practice of Christian apologetics is based on defending a belief. The practice of atheist apologetics is based on attacking a belief.
Christianity teaches absolute truth based on the unchanging word of God. Atheism teaches relative truth based on the changing scientific consensus.
Christians look to God's word as their objective moral standard. Atheists have no objective moral standard, so whenever they discuss morality (which cannot be accounted for in their naturalistic worldview) they must steal from Christians.
Christianity offers purpose and meaning in this world and hope beyond. Atheism offers none of the above, yet atheists continue to proselytize.