Ah, a very well-known Psalm. At first I wasn't a huge fan of it because it was that one Psalm that leaked into popular culture. However, after really getting time to read it later on I became much more endeared to it.
The beginning is what I really love "The Lord is my shepherd, I shall not be in want." There are so many ways to see that. Either I should not have any sort of want, because God's with me--or that God takes care of me so I'm not in want--or that God is all I want to begin with. This is something I really try to embrace throughout my life--all three interpretations of it.
I shouldn't be in want, because after all He "has given us everything we need for life and godliness" (2 Peter 1:3 NIV). But also, another way to see it is that I am simply not in want because God has provided for me. And likewise, in Genesis God describes Himself to Abraham (who was then called Abram, before God changed his name to Abraham) as his "very great reward" (Genesis 15:1 NIV).
Some people might find it hard to wrap their minds around that sort of concept, but the thing is that you're supposed to wrap your heart around it. As I've prayed more and have given more of my time to God and to His Word, I've found that God ultimately is the one thing that I desire more than anything. He really is my very great reward. And ultimately, being with Him in Heaven is the one thing I look forward to most.
Anyway, I just sort of rambled there. But that's kind of why I love the beginning of that Psalm.