"The ultimate ground of Christian Hedonism is the fact that God is uppermost in His own affections:
The chief end of God is to glorify God and enjoy Himself forever
The reason this may sound strange is that we are more accustomed to think about our duty than God's design. And when we do ask about God's design, we are too prone to describe it with ourselves at the center of God's affections. We may say, for example, that His design is to redeem the world. Or to save sinners. Or to restore creation. Or the like.
But God's saving designs are penultimate, not ultimate. Redemption, salvation, and restoration are not God's ultimate goal. These He performs for the sake of something greater: namely, the enjoyment He has in glorifying Himself. The bedrock foundation of Christian Hedonism is not God's allegiance to us, but to Himself.
If God were not infinitely devoted to the preservation, display, and enjoyment of His own glory, we could have no hope of finding happiness in Him. But if He does in fact employ all His sovereign power and infinite wisdom to maximise the enjoyment of His own glory, then we have a foundation on which to stand and rejoice."
Turns out, according to Calvinists, that God is quite narcissistic. I'm almost stunned by the acceptance that God would create such a breath-taking universe and set up such a marvelous plan of redemption, ultimately merely for Himself. No. There's more to it than that. God maximizes His enjoyment and glory in seeing His children become more than we are now--more than we could ever become without Him. In short, God's work and glory is us! "For behold, this is my work and my glory—to bring to pass the immortality and eternal life of man." (Moses 1:39).
He takes joy in helping His children advance and become like Him, one with Him. Now that is true love and grace. That is certainly a reason to be filled with ultimate gratitude, love, and praise. Yes, God is superlatively great, but He's not selfish. Similarly to how I take the most satisfaction from seeing my own children learn and grow, I deeply believe He receives His chief pleasure by watching and helping his own children grow and become like Him. Through the enabling power of the Atonement of Jesus Christ, we can become exalted through His grace, sharing in His quality of life. That, to me, is the chief end of God--not egotistically taking pleasure in Himself.