As a secular unbeliever, I also recognized the value of selflessness. I typically praised, for example, those who served and sacrificed, even when they didn’t have to. But is this form of selflessness simply a naturalistic, evolutionary adaptation, or is this virtuous principle the result of something even more transcendent than evolution? I think there is a better explanation for such behavior: selflessness points most reasonably to the existence of the Christian God.
On the other hand, if Christianity is true, selflessness is to be expected as the truest expression of the Christian God. Unlike other deities described in competing theistic worldviews, the Christian God is uniquely sacrificial and gracious. He doesn’t simply give us what we deserve. Instead, He extends kindness beyond the limits of our merit and gives us what we don’t deserve, even when there is nothing in it for Him. “Grace” is unmerited favor; the truest and purest expression of selflessness. No other theistic system proposes such a God. In every other religious system, adherents earn their salvation through some form of “good works”: they do something for God, then God responds by doing something for them. There is no gift involved, simply the payment for services rendered. In these systems, believers act with an expectation of return. This is not true selflessness. The Christian worldview encourages believers to act without an expectation of return: act, even though your actions may be completely unrewarded. The Christian God acts first in this selfless behavior by offering salvation as a free gift, in spite of our unworthy, undeserved condition. This kind of selfless grace is what separates Christianity from every other theistic worldview.
Why do we value selflessness when such behavior typically results in decreased survivability? Because we have been created in the image of God. Not just any God, but the one God who can truly account for selflessness. Selflessness points most reasonably to the Christian God of the Bible.