What is the Liturgy? The Liturgy is the customary way in which we worship God. It comes from Greek, and literally means "the work of the people."
Mass is a sacrifice because every time there is a mass, we recreate the death of Jesus on the cross in that the bread and wine become his own body and blood. This is his sacrifice, which is given to us at mass every time we go.
Liturgy and community are tied together because we as a community participate in the liturgy, or mass. As the rubric dictates, we respond to the priest in certain ways and do certain things. The liturgy itself cannot be complete without community.
Liturgical diversity means that the liturgy is different based on who its audience is. Since the church is very diverse, the liturgy has been molded to people all around the world so that they may worship in their own way and language.
The Church is both united and diverse because all Catholics have the same beliefs, but they do not have the exact same Liturgy. For example, in France, most churches will have mass in French, while in the United States, we celebrate mass in English.
I have neither given nor received any unauthorized help on this work. -Sebastian Tomaselli, 3/1/17, Period C