True Distinguishing Marks of the Church
The primary and most eminent distinguishing mark is purity of doctrine--doctrine consistent with the Word of God. We are not now dealing with those who deny fundamental principles, but rather with those denominated as Christians who acknowledge God's Word to be the infallible truth. We must therefore consider how God's Word defines the distinguishing marks of the true church. Let him depart who does not wish to conduct himself according to God's Word. However, he who wishes to esteem the Word of God as the only rule of life and doctrine will be able to perceive from this Word that only that church is the true church which has the true doctrine, consistent with the Word (II: 30).
Secondly, one would be in much greater danger of error if one were to depend on the mere testimony of an assembly, since false churches also claim be to the true church. Consequently one must have an infallible and dependable distinguishing mark which is free of error and cannot cause one to err. This is only true for the Word of God. If one therefore hears a church make claim of being the true church, and one examines doctrine and life by this Word and finds them to be in harmony with it, one can say with the believing Samaritans, "Now we believe, not because of thy saying: for we have heard Him ourselves, and know that this is indeed the Christ, the Saviour of the world" (John 4:42). It thus remains certain that the Word is the true distinguishing mark by which it is ascertained which church is true (II: 34).
If holiness is a distinguishing mark of the church, we will be able to identify the church by the same, and thus a church where true holiness is absent is not the true church. Other churches also boast of holiness, but all that is called holiness is not holiness. Therefore we must first determine from God's Word what true holiness is (II: 35).
True holiness springs forth from true faith. Where true faith is absent, true holiness will likewise be absent. Faith receives Christ as Surety unto justification and sanctification (John 1:12). By faith the soul is truly united with Christ (1 Cor. 6:17). By faith Christ, who is their life, dwells in their hearts (Eph. 3:17). Faith purifies the heart (Acts 15:9). Faith worketh by love (Gal. 5:6), and faith causes them to bring forth good works (James 2:18) [II: 35].
We hold the third distinguishing mark of the true church to be the proper administration of the Sacraments. Again this must be determined from the Word of God, and thus not be viewed independently but rather in conjunction with the other distinguishing marks. Wherever the first distinguishing mark is to be found, the others will be found likewise (II: 36).
These keys must not be used independently, however, but in conjunction with all the other distinguishing marks; their correct use must be determined by the Word of God. If those who err in doctrine and lead offensive lives are excluded, whereas those who are orthodox in doctrine and godly in their walk are included, the keys are used correctly; and by this one will be able to identify the true church. If anyone is included, however, regardless of what their doctrine and life may be, or if those are excommunicated who are orthodox in doctrine, while including in the fellowship of the church those who err, then such a practice is very evidently a mark of the false church. As imperfection is to be observed everywhere, and since this accompanying imperfection does not nullify the matter itself, there is also imperfection in the use of these keys. Although in one particular church these keys are used more consistently than in another church, one will find the proper use of the keys in the church (II: 36, 37).