David understood the importance of faith.  The background to this psalm is an incident in which David faced an adversary, and pretented to be insane so that he might be released.  You might say David used deception, and while that was true he also understood that the challenges of life require an abiding relationship with God.

This relationship is lived out in faith, even as we go through the journey of life.  Each and every day can be a challenge to overcome the obestacle that life presents us.  David reminds us that to come to God is to find the finest and best that there is, so that even in the midst of suffering we know peace.

It may be difficult to determine what "lacking no good thing" means, but we can be sure that nothing that we need will ever be lacking.  We have a part in life's journey, and must do our part if we are to make progress.  However, we can be sure that God will always do His part and keep us in his grace.