WHY we are in this suffering world?

Romans 14:8 For whether we live, we live unto the Lord; or whether we die, we die unto the Lord: whether we live therefore, or die, we are the Lord's.
Why are his children still wandering here and there through the suffering  maze, when a solitary word from his lips would bring them into the center of their hopes in heaven? 
The answer is--they are here that they may "live unto the Lord," and may bring others to know his love. We remain on earth as sowers to scatter good seed; as ploughmen to break up the uncultivated ground; as heralds publishing salvation. We are here as the "salt of the earth," to be a blessing to the world. We are here to glorify Christ in our daily life. We are here as workers for him, and as "workers together with him." Let us see that our life answered its end. Let us live earnest, useful, holy lives, to "the praise of the glory of his grace." Meanwhile we long to be with him.

(Spurgeon)