The fact that a man would be willing to lay down his life for his friend has nothing to do with whether or not a person is Christian. There are many examples in history where atheists and pagans have laid down their life for a friend or loved one. The name of many a law enforcement officer, soldier or parent has been inscribed on a tombstone because they were willing to give their life to save another. Regardless of the fact that one was willing to make the ultimate sacrifice in order to spare the life of another does not necessarily mean that religious faith was a motivating factor.
Divine love is far different from human love.
The difference is that Christ was willing to lay down His life for His enemies. But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Such love is not human. Such a statement is totally foreign to those whose thinking is infused with a belief in the evolutionary process. They have no understanding of or see no need for redemption or regeneration.