For a long time I took this to mean sacrifice, something I seemed to want but I should not have. If I were to get “it”God would be angry and punish me. Actually the Psalmist is telling me “thou can’t …” want. That have already been given all by All . Everything God is, I am, save one thing: I’m not God.
God asks no sacrifice. He/She only asks that I remember who I am and be happy, as He created me. “I am as God created me.” I shall not want, for I have everything And everything is All, forever. I need to look out at the world and say this very truth to everyone. Love comes easy. Grievances not so.
However, God never lets us off the hook with our nonsense. What I want in the world I made God interprets gently and sees to the steps I must take to change course. What I want I don’t need, can’t have, or would discard if I got it. It is that way with wants. It is why I “shall not want.” The everything forever is all described for us in the rest of the psalm.