There are different levels of pleasure. Each is precious. The lowest level is physical joy. If the source of this joyful experience is kosher, then the joy that comes from it is a gift from Hashem given to us so we will enjoy His creation. Hashem wants us to enjoy His world. Delicious food is a good example of a source of physical pleasure.
The next higher level of joy is emotional joy. When you see your loved ones it brings a warm, joyful feeling to your emotional heart. This joy is more precious to you than even the joy that delicious food brings.
Still higher than emotional joy is intellectual joy. Imagine working on a project for a year trying to solve a major, worldwide problem. Then finally the answer comes to you. The accompanying joy is far greater than either physical or emotional joy. This is not to say that those lower joys are not precious. It shows that intellectual joy is even more meaningful.
There is another level of joy that greatly surpasses these. This is the spiritual joy that comes when one is blessed to receive even the slightest glimpse of Hashem's Revealed Presence. This experience fulfills your purpose in having been created, and the joy that comes with it is so intense that if the experience were to continue beyond a brief moment the soul would soar up, forsaking the body.
But how do we even dream of bringing such an experience into our lives? Food I can buy. Family I can make. Intellect I can work on, but how do I bring about this highest of all joys?
First look at the opposite to see what not to do. There is one sin so evil that if (G-d forbid) a Jew would do it Hashem would curse that Jew 98 times… one after the other, each curse worse than the one before!
What did that poor Jew do to bring these curses? "All these curses came upon you because you did not serve Hashem with joy…"[i] It does not say the curses came because he did not serve Hashem. He was serving, but he was not happy doing it. Don't do that one! When you do a mitzvah you have to be happy.
The Torah is not referring to the happiness that comes from jumping up and down. It is talking about the joy that comes from understanding that you are serving the Holy One and fulfilling His wishes for you. What could possibly bring more joy than that? Hashem's Revealed Presence is only experienced in joy.
Just as we are to serve Hashem every day, so too must we be joyful every day. If you are not happy, you are doing something wrong. The Zohar says, "Just as did G-d put Adam (the First Man) in the Garden (Eden) back then, so does He put man in the Garden today, when he busies himself with Torah and mitzvahs."[ii] This is the Garden of Eden, right where we are living today.