Each local church is an outcrop of the one universal church and will embody the nature of that church as the Father’s regenerate family, Christ’s ministering body, and a fellowship sustained by the Holy Spirit. The world contains self-styled churches with doubtful or false credentials (e.g., the Unitarian churches and the Mormon church, both of which deny the Trinity). Furthermore, congregations that once held the faith unambiguously have been known to lapse to the point where it is hard to know if they are churches anymore. Discernment is therefore necessary. As they opposed the papacy and separated from the Roman Catholic church, the Reformers needed to determine the marks of the true church. From Scripture, they found the answer in terms of two criteria.

1. The faithful preaching of the Word of God. This means that the group in question teaches from Scripture the essentials of the Christian gospel. Denials of the Trinity, the deity of Christ, the sin-bearing atonement, and justification by faith, for example, link aberrant contemporary groups with the docetic separatists, whose denials of Incarnation and Atonement (1 John 4:1-3) caused John to say, “They did not really belong to us” (1 John 2:19).
2. The right use of the sacraments. This means that baptism and the Lord’s Supper are seen and explained as setting forth the gospel so as to evoke, confirm, and strengthen faith in Christ. Superstitions that stifle faith by turning the sacraments into magic rites are intolerable. Such superstitions strike at churchly identity in a radical way, as does anything else that obstructs faith in Christ. Reception into the visible church is part of what being baptized means; confirmation of one’s place in it is part of what sharing in the Lord’s Supper means. Right use of the sacraments involves an element of church discipline whereby professions of faith are tested and public behavior is reviewed.

Ideally, a Christian congregation will exhibit other marks of its identity alongside these minimal two. Luther specified the keys of discipline (Matt. 16:19), an authorized ministry (Acts 14:23; 20:28), public worship (Heb. 10:25), and suffering under the cross (Acts 14:22; 20:29). The Reformed churches specified a functioning system of discipline and have spoken of discipline as a third criterion or mark of the visible church (Titus 1:13; 2:15; 3:10). Charismatics and others today specify the active ministry of every member as another mark of the true church (Eph. 4:7-16).

These additional marks are not, however, essential in the way that the minimal two are. A church that lacks them is certainly deficient, but it would not be true to say that it is not a church at all.