A revelation, that may be supposed to be really of the institution of God, must also be supposed to be perfectly consistent or uniform, and to be able to stand the test of truth; therefore such pretended revelations, as are tendered to us as the contrivance of heaven, which do not bear that test, we may be morally certain, was either originally a deception, or has since, by adulteration become spurious.
Reason therefore must be the standard by which we determine the respective claims of revelation; for otherwise we may as well subscribe to the divinity of the one as of the other, or to the whole of them, or to none at all.
Ch. XIII Section II - Of The Importance of the Exercise of Reason, and Practice of Morality, in order to the Happiness of Mankind - Reason: The Only Oracle Of Man (1784)