In answer to your question, “Do not the bounds of Scriptural communion extend to all who are real Christians, except their practice is immoral, or they have embraced dangerous heresies?”
There are three different grounds on which mixed communion is defended—1. That baptism is not essential to church communion. 2. That, if it be, adult immersion is not essential to baptism. 3. That, if neither of these be true, yet the right of judging what is and what is not baptism lies in the individual, and not in the community. The statement of your question proceeds upon the first of these grounds; to this, therefore, I shall confine my answer.
I observe you do not plead for communion with saints as saints; for, if so, you could not refuse it to any one, unless you thought him a wicked man: whereas your question allows that real Christians, if they are guilty of immorality, or if they have embraced dangerous heresies, ought to be excluded. This they doubtless ought to be, and that partly for the honour of God, and partly for their own conviction. They are a kind of lepers, whom the people of God should require to be without the camp.
You admit that there are cases in which it is right for good men to be kept from church communion; but you conceive that this should be limited to cases of immorality and dangerous heresy. If there be any difference then between us, it lies in your omitting to add a third case, viz. an omission or essential corruption of instituted worship. Without this, I do not see how you can justify your dissent from the Church of England, or even from the Church of Rome, provided you agreed with them in doctrine and in morals and were satisfied respecting the piety of your fellow communicants.
You must admit that, so far as primitive example is binding, it has every appearance of establishing the necessity of baptism previously to communion; all that were admitted to church fellowship were in those times baptized. And it appears that the one was considered as necessary to the other. John, the harbinger of Christ, came to “make ready a people prepared for the Lord,” (Luke 1:17,) or to prepare materials for the kingdom of heaven, which he announced as being at hand. For this purpose he “baptized with the baptism of repentance,” (Acts 19:4,) saying unto the people that “they should believe on him who should come after him, that is, on Christ Jesus,” Acts 2:42. In other words, his object was to render them Christians and to baptize them. It was thus that they were “prepared for the Lord,” or rendered fit materials for gospel churches. Peter said, “Repent, and be baptized, every one of you.” Paul, in all his Epistles, takes it for granted that all Christians were baptized, Rom. 6:3, 5; Eph. 4:5; Col. 2:12; 1 Cor. 1:13; 12:13. When baptism and the Lord’s supper are alluded to, it is in connexion with each other, 1 Cor. 10:2–4.
You do not pretend that any of the primitive Christians were unbaptized. All you allege is from analogy, or that the apostles dispensed with various other things, which you suppose to have been of equal importance; and that, therefore, if some at that time had neglected to be baptized on some such principle as that on which the Quakers now neglect it, they would have dispensed with this also. It is acknowledged that they did dispense with a uniformity in matters of circumcision and uncircumcision, of days, and meats, and drinks, and whatever did not affect the “kingdom of Christ,” Rom. 14:17. But it appears to me very unsafe to argue from abrogated Jewish rites to New Testament ordinances, especially as the one are opposed to the other. “Circumcision is nothing, and uncircumcision is nothing, but the keeping of the commandments of God,” 1 Cor. 7:19. Nor does it appear to me, from any thing that is said on the doctrine of forbearance in the New Testament, that the apostles would have dispensed with the omission of baptism. The importance of this ordinance, above every thing dispensed with in the primitive churches, arises from its being the distinguishing sign of Christianity—that by which they were to be known, acknowledged, and treated as members of Christ’s visible kingdom: “As many of you as have been baptized into Christ have put on Christ,” Gal. 3:27. It is analogous to a soldier on his enlisting into his Majesty’s service putting on the military dress. The Scriptures lay great stress upon “confessing Christ’s name before men” (Matt. 10:32); and baptism is one of the most distinguished ways of doing this. When a man becomes a believer in Christ, he confesses it usually in words to other believers: but the appointed way of confessing it openly to the world is by being baptized in his name. If, therefore, we profess Christianity only in words, the thing professed may be genuine, but the profession is essentially defective; and as it is not Christianity, (strictly speaking,) but the profession of it, which entitles, us to a place in Christ’s visible kingdom our claim to visible communion must of course be invalid.
Baptism is an act by which we declare before God, angels, and men, that we yield ourselves to be the Lord’s; that we are dead to the world, and, as it were, buried from it, and risen again “to newness of life,” Rom. 6:3, 4. Such a declaration is equal to an oath of allegiance in a soldier. He may be insincere, yet, if there be no proof of his insincerity, the king’s officers are obliged to admit him into the army. Another may be sincerely on the side of the king, yet, if he refuse the oath and the royal uniform, he cannot be admitted.
To treat a person as a member of Christ’s visible kingdom, and as being in a state of salvation, who lives in the neglect of what Christ has commanded to all his followers, and this, it may be, knowingly, is to put asunder what Christ has joined together.—See Mark 16:16. “He that believeth and is baptized shall be saved, but he that believeth not shall be damned.” By this language he hath bound us; though, not having said “he that is not baptized shall be damned,” he hath mercifully refrained from binding himself.
Fuller, A. G. (1988). “Thoughts on Open Communion,” in The Complete Works of Andrew Fuller: Expositions—Miscellaneous (J. Belcher, Ed.; Vol. 3, pp. 503–505). Sprinkle Publications.