This is the mission of the church, to announce to the world the good-news of salvation. The world needs to hear the message of salvation, so they can make an eternal choice. Jesus has given the job of presenting the Gospel to those who are “Saved”.
The promise of eternity is clear in scripture; we are made in the image of God (Gen. 1:26-27). Since we are in God’s image, we are eternal, whether we like it or not. God made us this way, eternity is promised in scripture to both saved and lost.