He does not say this to be morbid or fatalistic, but to put our lives into perspective before God and remind us of our only ultimate hope. We are made of mortal stuff. We belong to time, and only God can offer us the gift of the eternal. And how we wait makes all the difference in the world. We can stop, stand still, give up, passively wait for God to do something or circumstances to change because of what others do for us or maybe, against us.
Materialism is the ultimate expression of despair.
Or we can make use of the time we have to be better prepared when the day comes and the goal is reached and the waiting is over. We can either get busy living or get busy dying. It is important for us to be waiting and working. But there were a few who learned a great lesson about God because of the exile. Some of the most important spiritual experiences are born out of the most difficult times in our lives.