Christians are those who think that they do not have to take the meaning of their lives from the the present political and social arrangements, but from a "world to come," the kingdom of God, which they trust will come. The central Christian doctrine is the resurrection of the body -- Christ is "the first-born from among the dead" (Paul) --"as he is, so shall we be."
The ethic that Christians take from this is not particularly optimistic; they say that if you do not love, you will not be alive, but if you love enough, you will be killed; but God will reverse the judgment of the world. The earliest extant Christian document describes Christians as "those who have hope," and that seems to me quite near the center of the gospel.
The most committed, devoted Marxist, who firmly believes in the historical inevitability of the arrival of pure communism after the sacrifice of many generations -- still has the burden of thinking of all of those who died in agony (or simple meaninglessness) before that blessed state arrived. The Christians are less puritan: they want it all, and they want it forever, and for everybody.
But, as the apostle Paul says, "If Christ has not been raised, your faith is futile and ... we are of all people most to be pitied." --CGE