Why would God want us to praise and worship Him? This is a question I hear every so often since we immediately assume that a person who demands praise is a pompous big-head. I think there are many Christians out there who secretly wonder about this—afraid to ask the question (lest they be thought unspiritual), but bothered all the same.
God is completely self-sufficient and doesn't need our praise and worship. However, He does deserve it. Would you agree that it is right and good to praise someone who is worthy of praise? We instinctively know this and praise people for all sorts of achievements. We praise the people we love and admire, and it's not right or good for us to withhold praise from them.
We all understand the concept of praise being due certain people. Imagine that you crafted an incredibly beautiful sculpture and won a prestigious award for your creation; but when the time came for the award ceremony, they gave the prize for your sculpture to the wrong artist! That would not be just, right, or good. In the same way, God—as the only being perfect in goodness, justice, love, etc.—is worthy of our praise. We do, in fact, owe Him that praise. He wants us to praise Him because it is right and good for us to do so. Since God wants us to do right and good things, of course he wants us to praise and worship Him.
Beyond the praise being right and good (and because of its being right and good), worshiping God also brings us joy and enhances our relationship with Him. We see this in human relationships as well—think of a man with his wife. Doesn’t it bring him great joy to praise her?
Here's how C.S. Lewis puts it in Reflections on the Psalms:
I had never noticed that all enjoyment spontaneously overflows into praise…. The world rings with praise—lovers praising their mistresses, readers their favourite poet, walkers praising the countryside, players praising their favourite game…. I had not noticed either that just as men spontaneously praise whatever they value, so they spontaneously urge us to join them in praising it: 'Isn't she lovely? Wasn't it glorious? Don't you think that magnificent?' The Psalmists in telling everyone to praise God are doing what all men do when they speak of what they care about. My whole, more general, difficulty about the praise of God depended on my absurdly denying to us, as regards the supremely Valuable, what we delight to do, what indeed we can't help doing, about everything else we value. I think we delight to praise what we enjoy because the praise not merely expresses but completes the enjoyment; it is its appointed consummation. It is not out of compliment that lovers keep on telling one another how beautiful they are; the delight is incomplete till it is expressed.
Finally, God created us for His pleasure (just as we create delightful things for our pleasure). Praising God—acknowledging His goodness, love, perfection, and all the incredible things He has done for us—brings Him pleasure. If you have children, you know what a beautiful thing it is to have them praise you. You also know the pain of having them selfishly take you for granted and ignore you. When that happens, neither you nor your children are enriched, and your relationship is strained. In the same way, the right response from us toward God is praise because He deserves it. When we act out our love and acknowledgment of Him in this way, we fulfill our purpose; and when we are rightly fulfilling our purpose, we have the best possible joy—God is pleased, our relationship with Him is enhanced, and He has rightly received what He deserves. Luckily, this is not a difficult command to follow, for when we truly love Him, our praise will flow naturally from that love.