"And [if you] call the Sabbath a delight, the holy day of the LORD honorable . . . Then you shall delight yourself in the LORD . . . "
How does one "delight" oneself "in the Lord"? Or, to put it another way, "How does any human being experience the truest, highest, and most lasting and satisfying pleasure?" Answer: by delighting in the *same* things God Himself does.
The Lord delights in seeing faith and repentance in people, which manifest themselves immediately in love for Sabbath (Sunday), church, and worship. Do you want to be happy, like God is? Then adopt His values, His priorities, and His love-objects.
[Puritan quote of the day: "We must keep grace in exercise. It is not sleepy habits, but grace in exercise, that preserves us." --Richard Sibbes, in "The Bruised Reed"]