Door Mr. Brian P. David
No one would dispute the fact that these beautiful words have a deeper meaning. Obviously, we are not literally sheep, and the Lord is not literally a shepherd. But this is not just poetry; the words have a specific spiritual meaning.
According to the Writings, a shepherd represents someone who teaches people what they need to know to live a good life, and leads them toward that life. To "want" for something means that you lack the knowledge and the inspiration you need to live that good life.
What this verse means, then, is that if we turn to the Lord for knowledge, guidance and leadership, we will get what we need to lead a good life.