Preamble: What we share

Before this guide describes how churches differ, it starts with what the people in them share.

Jesus prayed for his followers to be one. On the night before he died, he prayed not only for his first disciples but "also for those who will believe in me through their word" (John 17:20). That includes every believer since. He asked "that they may all be one, just as you, Father, are in me, and I in you," and he gave the reason: "so that the world may believe that you have sent me" (John 17:21; see also 17:23). Our oneness is meant to be seen. The world is watching how Christians treat each other, and Jesus tied the world's belief in him to what it sees.

What believers share. Whatever church we belong to, most of us confess together one God in three persons; Jesus, fully God and fully man, who died for sinners and rose from the dead; the Bible as God's word; and a hope in Christ's return. Paul gives the list in short form: "one body and one Spirit… one hope… one Lord, one faith, one baptism, one God and Father of all" (Ephesians 4:4–6). Christ alone is the head of this body (Ephesians 1:22–23; Colossians 1:18). This guide cannot say who belongs to his body, because "the Lord knows those who are his" (2 Timothy 2:19). Christians also disagree about how that body relates to any one denomination (see the extra question on the Church and salvation). What the guide can do is describe what churches teach, so that you can find a congregation where you can live out your place in the body.

Unity and uniformity are different things. Unity is a gift God gives. Jesus prays for it, and Paul tells us to be "eager to maintain the unity of the Spirit in the bond of peace" (Ephesians 4:3). We guard what he gives. We do not build it by making everyone alike. Uniformity is sameness kept up by pressure, where everyone worships, votes, and thinks alike on everything. Unity is a shared life in Christ that can hold real differences. Paul's picture is a body with many parts: "If the whole body were an eye, where would be the sense of hearing?" (1 Corinthians 12:17).

Unison and harmony. Music gives a way to think about this. In unison, everyone sings the same note. It is clear and strong, and it fits some moments, such as saying a creed together. In harmony, different voices sing different notes at the same time, and the sound is richer than any single voice. Harmony is not a free-for-all. The voices need a shared key and the same song. For the church, the shared key is Christ and the gospel. Jesus' prayer asks for both oneness and truth: "Sanctify them in the truth; your word is truth" (John 17:17). A note that leaves the key does not add to the harmony, which is why Scripture also warns against a gospel that is not the gospel (Galatians 1:8). The Bible uses both pictures. Believers are to glorify God "with one voice" (Romans 15:6), and they are one body of many members with many gifts (1 Corinthians 12). So the church needs something like unison for what it confesses together, and something like harmony for how that faith is lived out in different callings, cultures, and traditions. Where one ends and the other begins is part of what Christians disagree about.

Reading Scripture well without a theology degree. You do not have to study theology to read the Bible well. You do have to know who is helping you read. Judgment (the author's): the Bible is the ultimate source, and a church serves as an interpreter of it. A church hands on readings that many people have tested over a long time against the whole of Scripture. That is a check on a familiar danger, which is taking a verse out of its context and building a belief on it alone. A reader alone with one verse has no one to say, read what comes before and after it, or this question has been asked before. A church is not a perfect check. It can hold a wrong reading firmly, and churches differ on how much weight their readings should carry, from binding to advisory. The guide records each church's answer to that (Q2, and how firmly the church holds its people to its teaching). So choosing a church is, in part, choosing an interpreter. The questions to ask are who decides what Scripture means here, and who can correct that decision (Appendix B, Findings 13 and 15). The reader's part stays the same: test what the church teaches, and what you hold, against Scripture and in prayer.

How this guide uses that. The common-ground items (Q0) are the shared key. Everything after them records parts: places where faithful believers sing a different line of the same song, such as how a church is governed, how often it takes communion, or who may be an elder. Churches also differ on what belongs in the shared key itself. For example, Catholic and Orthodox churches state some common-ground items differently, and some groups would add items that others treat as secondary. The guide records those differences plainly and does not settle them. The six common-ground statements appear in the questionnaire as Q0. They are not scored, because they are the shared key and do not sort one church from another; each church's profile records how its own documents state them. It does not say which differences are small and which are large. Paul says to welcome those who differ on disputed matters "but not to quarrel over opinions" (Romans 14:1), and to "pursue what makes for peace and for mutual upbuilding" (Romans 14:19).

Why this matters. The purpose of this guide is to help you find your place in the body of Christ, where Christ is the head, and to serve the people near you. It is not to sort believers into camps or to win arguments. The world is watching. A guide that compares churches should leave believers better able to love each other, not less.