[T]he Church is a Divine institution, owing its origin not to man, but to Christ, and associated together not in consequence of human arrangement, but by Christ’s appointment.
No doubt there is a foundation laid in the very nature of the religion which Christ came to promulgate, for the union of His disciples in one body or society. The faith which each man holds for the salvation of his own soul is a faith which joins him to every other believer. The close and mysterious union which is constituted by faith between him and his Savior, is a union that connects him through that Savior with every other Christian. In becoming one with Christ, he becomes at the same time, in a certain sense, one with all who are Christ’s. The spiritual fellowship that a believer enjoys with his Redeemer, is not a solitary or a selfish joy, but one which he cannot possess alone, or except in common with other believers. It is the very nature, therefore, of the Gospel to be not a solitary religion, but a social one. When Christ, through the mighty operation of His Spirit, brings a sinner into reconciliation and communion with Himself, He ushers him also into the fellowship of reconciliation and communion with all other Christians. When the work of grace is done upon the soul of man, and the barriers of separation between him and his Savior are cast down, and the sinner who was afar off is brought near to God, the very same work of grace removes the obstacles that hindered his union to his fellow-believers. Were there no positive command or appointment, therefore, requiring Christians to unite together and to form on earth a society joined together by the profession of the same faith, the very nature of Christianity would force such a result.
– James Bannerman, The Church of Christ, pp. 19-20 (emphasis added).