One of my political heroes is William Wilberforce, whose faith led him to a years-long crusade to end the British slave trade. Among other things, he was an animal rights activist. One can understand why he had purpose in his life. He saw his limited time on earth as an opportunity to do something eternal.
Wilberforce was, in his mind, at least, fulfilling an ordained mission. But the atheist must see himself more like Sisyphus, who is rolling the rock up the hill each day, for no apparent reason.