In Psalm 50, God says he wants everything, because he wants nothing. He wants your sacrifice, because he doesn't need your sacrifice. This makes no sense; or it makes all the sense in the world if you understand that religion and worship are not the same thing.
God calls Israel to judgment, "Not for your sacrifices do I rebuke you; your burnt offerings are continually before me" (Psalm 50:8). Okay, you are religious, says God. Let's examine your religion. "Offer to God a sacrifice of thanksgiving, and perform your vows to the Most High, and call upon me in the day of trouble; I will deliver you, and you shall glorify me" (Psalm 50:14-15). Your religion is a formula. You give God what he needs; he gives you what you need. You're using God to serve yourself.
But, "every beast of the forest is mine, the cattle on a thousand hills," says God. "I know all the birds of the hills, and all that moves in the field is mine" (Psalm 50:10-11). God doesn't need anything. The formula doesn't work. Now what?
Now you can worship. You can give God everything because he needs nothing, and therefore you can trust him fully. What are you giving him that isn't his already? Yourself, and that is worship.
Father in Heaven, The world is Yours, and all that is in it. You are the source of every good and every blessing, and the greatest blessing is I am Your son. You have adopted me back into Your family by making me righteous again through the saving work of Your Son. You call it grace. I call it good news.
You have given me everything, God. I give it all back. It's yours, all of me. Now tell me what to do!