For those in my '613' class, I hope this is a helpful summary of a reading that has been difficult for many people. For people not in the class - you might find the ideas in his book very useful.
Stone says that to be a human being is to live with a constant choice between good and evil and that this imposes a "terrible responsibility" on us (p 112).
Awareness of this responsibility brings what is traditionally called yirat hashem ("awe of God"). Fulfillment of our obligation - doing what is good - brings a sense of fulfillment and pleasure. In seeking out this pleasure we are experiencing ahavat hashem ("love of God").
To seek what is good we have to "choose the good of our neighbor." That is, we have to care about doing good for other people.
"This principle reaches us in the language of scriptural commandment: ve'ahavta le'rayakha kamokha, "You shall love your neighbor as yourself" (Leviticus 19:18)."
But why do we need all of the mitzvot - all the 613 commandments of Jewish life? Why not just take "love your neighbor as yourself" as a kind of general commandment, and use that to guide our lives. Wouldn't that inculcate the kind of responsible life that Rabbi Stone thinks is essential to Jewish life?
Stone argues that human beings want to run from the responsibility of being alive. We just want to be left alone when confronted with yirat hashem, awareness of our responsibility. The responsibility feels too much too bear, so we want to "go to sleep," as he puts it, and be relieved of responsibility. This is where the mitzvot fit in. The mitzvot
keep us awake to our...obligations. Moreover they allow us to invoke the community to share the burden that...would otherwise be all our own. (114).So, two points here. First the hundreds of mitzvot help create a kind of mindfulness (he calls it wakefulness) that keeps us attuned to our responsibility as human beings. This is why he says the mitzvot are important in mussar. The mitzvot remind us and help us to live with the middot.
The second point is that Jewish life is communal and that helps us share and endure the burden of yirat hashem. For example, the responsibility to care for those who are ill is an overwhelming responsibility for one person. But because it is a communal obligation, we share in the responsibility and help one another fulfill it.