On p. 14 he explains:
'Liturgy' comes from a Greek word meaning "a public service." When I refer to "the liturgy" in this book, I am referring to the public Sunday service performed by liturgical and mainline churches.
On p. 18:
So, the liturgy teaches us ABOUT the story, especially in Word and Sacrament. But it does more. It also EMBODIES the Christian story in its very structure - God gathers people for a great banquet at which he presides, gives us a Word, and offers us the fruit of his labor of love. From there, God sends us out to participate in the great gathering work.
By participating in the liturgy, we're doing more than "attending a service." We are entering a story - a story in which we also play a role. We are the people who have indeed been gathered. We are the people who share in God's very life. We are the people sent forth to proclaim God's story and to invite people into the grand story.