A book I would like to recommend to all who read here, is: One Lord, One Faith by Rex Koivisto (he was a prof of mine at Multnomah, who, among others, taught me Greek, Ecclesiology and Eschatology). This book deals with issues surrounding ecclesiology and its description relative to the New Testament, the role of Tradition in and for the church, sectarian attitudes, and more. It is a very helpful guide through this complex area of study. Here is how Koivisto opens up his Preface:

This book is about catholicity. It is not about Roman Catholicism, but about catholicity. Catholicity refers to the great universality of the church as the body of Christ—not just in some mystical sense, but in all the fullness of its “real-time” diversity on planet earth. And catholicity presupposes a large-hearted attitude on the part of Christians to perceive the church this way, because by definition it encompasses real believers who do not quite act or talk, or think, or even believe all the same things that I do on areas outside of the central tenets of the Christian faith. I am convinced that this precious quality has been significantly tarnished midst our sad assigning of each other into different Christian cubbyholes—a process that allows for little dialogue or mutual communication, and which tends only to decrease our ability to enjoy all we have in common with each other, “across boundaries,” in Christ. (Rex Koivisto, “One Lord, One Faith,” 13)

Koivisto is primarily a biblical exegete (a language guy) by training, and this becomes quickly apparent, as he inductively engages the New Testament (and Old) as the normative guide for understanding how Jesus, Paul, and the early church understood herself. I think you will find this an illuminating read, if you struggle or just wonder about such things. I am currently re-reading this text (last time was approx. 7yrs ago), so expect to see quotes and reflection on this issue down the road.