There are many different types of joy in the Bible. The joy Paul derived from Philemon, the joy of new human birth, and the joy over a sinner saved, rescued from the pits of hell.
Unexpected gifts, the first dip into just-opened peanut butter, books and rainy days. Joy from loving and being loved in return, joy that a son has returned from war, joy from a new pair of shoes or a new car.
Joy that God is love, that He is good, kind, and King. Joy that He listens, and answers, through silence, speaking, friends or enemies. Joy that regardless of disappointment, pain and suffering, He brings peace. Joy that in sickness, He heals. Joy that in broken relationships, He restores.
We find joy in things that benefit us. We rejoice with a soldier returned home not only because they live, but because that means our time with them on earth remains. We find joy in God being good because His being good means He offers salvation, a way out, a way up. We rejoice in His peace because it is greater than the suffering which it replaced.
I beileve the highest form of joy is that God IS. That is it; it ends there. Yes, He is good, kind, faithful, loving, gracious, wrathful, and just. And to have joy in those things is both acceptable and right. But to have joy that He exists, simply, is another thing altogether. "I am that I am," He says. A statement that is so beautiful, perhaps because we know that our finite minds can't scratch the surface of such an infinite statement.
As we express our joy to the Lord through prayer, an escalation occurs. As our minds race through the reasons we rejoice in Him, we can't help but reach a climax - we are joyful because He IS. Forget all the rest. We shout because You ARE. Because He exists, simply. Simply, yet how deep it is.
And as if God planned it from the start, even this highest form of joy goes not against the pattern that we rejoice in things that benefit us. Because the single greatest benefit to us is that He does exist.