One of the principles I appreciate about GTD, and often remind people when I'm counseling them about living more productivity for God, is that your list will never get shorter. God is always working, His kingdom is always advancing, the world is always decaying. So every time you cross something off, something new will appear. One of the first rules I share with people (and try to remind myself every day) is "Give up the fantasy of completion."
In my daily Bible reading, I came across this passage in Ecclesiastes which caused me to meditate, once again, on this principle:
All streams run to the sea,
but the sea is not full;
to the place where the streams flow,
there they flow again.
All things are full of weariness;
a man cannot utter it;
the eye is not satisfied with seeing,
nor the ear filled with hearing.
Ecc 1:7-8
The work I have to do in my life--for my job, for my ministry, for my family--is like the streams running to the sea, and sound going to the ear. If the stream had as its goal to fill up the ocean and be done, it would be sorely disappointed, and badly confused about its purpose. That doesn't mean that the stream's work isn't important; it's essential. It's just that the goal is not clearing my list, any more than the goal of listening to music or of looking at my wife as to fill my ears and eyes so that they don't ever need to listen or look again.
Praise the Lord for his wise and perfect Word, sufficient for every circumstance of life!