Our responsibility is to get God's word to their ears. Only God can get the word from their ears to their heart.
Hang on to this with your life: "In the world you will have tribulation. But take heart; I have overcome the world."
There is no Christian Gospel if history simply unwinds into a meaningless puddle, if the cosmos simply escapes into a cataclysmic black hole, or if the universe finally dies of exhausted energy. Without belief in a biblical eschatology, there is no Christian hope. Without a sense of perfect moral judgment in the end, the human heart is homeless.