Baptism is a Divine institution, pertaining to the kingdom of the Messiah, or the gospel dispensation. John received it from heaven, and administered it to the Jews, who, on his proclaiming that the kingdom of heaven was at hand, confessed their sins. Jesus gave sanction to it by his example; and after his resurrection, when all power in heaven and earth was committed to him, he confirmed and extended it to believers of all nations. Whatever circumstantial differences there might be, therefore, between the baptism of John and that of Christ, they were substantially the same. There were things in former ages which bore a resemblance to it; as the salvation of Noah and his family in the ark, the passage of the Israelites through the sea, divers washings or bathings prescribed by the Mosaic ritual, &c.; but the thing itself existed not, till it was revealed to the immediate forerunner of Christ.
The principal design of it appears to be, A solemn and practical profession of the Christian religion. Such was the baptism of John, who “said unto the people, that they should believe on him who should come after him; that is, on Christ Jesus.” And such was that in the times of the apostles. Paul addressing himself to the churches in Galatia, who, after having professed to believe in Christ, cleaved to the Mosaic law as a medium of justification, thus speaks: “The law was our schoolmaster to bring us to Christ, that we might be justified by faith; but after that faith is come, we are no longer under a schoolmaster. For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ.” The allusion is to the putting on of apparel, as when one that enters into the service of a prince puts on his distinguishing attire; and the design of the sacred writer is to remind those of them who had before professed the Jewish religion, that by a solemn act of their own they had, as it were, put off Moses, and put on Christ. There is a putting on of Christ which is internal, and consists in relinquishing the former lusts, and being of the mind of Christ; but that which is here referred to appears to be an open profession of his name, to the renouncing of every thing that stood in competition with him. It was therefore true of as many as had been baptized, whether they abode in the truth or not. And even their being “the children of God by faith in Christ Jesus” seems to express what they were in profession, rather than what they were in fact. They had by their baptism disowned all dependence on the privileges of birth, and the adoption which pertained to them as the children of Abraham; and declared their acquiescence in that power, or privilege, to become the sons of God, which the gospel imparts to them that believe. The mention of this was perfectly in point, as it greatly heightened the evil of their defection. The amount is, That as many as were, baptized in the primitive ages were voluntary agents, and submitted to this ordinance for the purpose of making a solemn and practical profession of the Christian faith. It was their oath of allegiance to the King of Zion; that by which they avowed the Lord to be their God. Hence a rejection of it involved a rejection of the counsel of God. The sin of the Pharisees and lawyers consisted, not in their refusing to submit to baptism as unbelievers; but in not embracing the Messiah, and so putting on the badge of his profession. Their rejection of the sign was justly construed as a rejection of the thing signified; as when a rebel refuses to take the oath of allegiance, it is construed as a refusal of submission and subjection to his rightful prince.
Such, brethren, is the profession we have made. We have not only declared in words our repentance towards God, and faith towards our Lord Jesus Christ; but have said the same things by our baptism. We have solemnly surrendered ourselves up to Christ, taking him to be our Prophet, Priest, and King; engaging to receive his doctrine, to rely on his atonement, and to obey his laws. The vows of God are upon us. We have even sworn to keep his righteous judgments; and, without violating the oath of God, we cannot go back. If it be a sin not to confess the Lord Jesus, through fear or shame, it is a still greater sin, after we have confessed him, to turn from the holy commandment.
The religion of Jesus consists partly of truths to be believed, and partly of precepts to be obeyed; and the ordinance of baptism furnishes motives for a faithful adherence to both.
Excerpt from: “The Practical uses of Christian Baptist” (1802), from the Circular Letters.
Fuller, A. G. (1988). The Complete Works of Andrew Fuller: Expositions—Miscellaneous. (J. Belcher, Ed.) (Vol. 3, pp. 339–340). Harrisonburg, VA: Sprinkle Publications.