Catholic Basics:
>This book is a theological study of the Church, that is, an ecclesiology. There is a rhythm at work in the eucharistic Liturgy and thus in the Christian life as a whole that provides us with a key insight for understanding the Church. In this dynamic movement of coming together and going forth, symbolized in the rites of gathering and dismissal that frame the Mass, we have the basic elements for a theology of the Church. In theological categories, those basic elements may be termed "communion" and "mission." Reflection upon our ongoing experience of communion and mission can thus provide us with a vision of what it means to be the Church.
--From chapter 1