Because it is contained in Scripture, "Behold, I lay in Zion a chief cornerstone, chosen, and precious: He who believes in him will not be disappointed."
So live a life that is a witness before the world. They may say ugly things to you. They may sneer at you. They may mock you. But let your life be a witness that when the Lord raptures you, they're going to say, Wow, that guy was right, you know. He was really a neat guy, you know, he was all right. He did the right thing, you know, oh man. So, they will.