As some know, I have an interest in the Christadelphian faith (a Unitarian Restorationist group from the 19th century). While reading the letters their founder John Thomas (1805-1871) wrote to Alexander Campbell, we have an early witness to Thomas' rejection of baptism being regenerative/efficacious ex opere operato and his belief that the efficacy of water baptism is strongly contingent upon one's then-present knowledge:
Again, there
are those who (in effect) say that immersion in water, abstractly considered,
is baptism, and that as there is but one baptism, and not two, immersion ought
not therefore to be repeated. Now these persons, profess to believe in
baptism—with them immersion—for the remission of sins; hence they must suppose
that water washes away sins, which is of all absurdities the most absurd! “The
garment spotted by the flesh” is purified, or washed white, in the blood of the
Lamb, not in the water abstractly regarded. Such objectors need to be taught
the first principles of the doctrine of Christ; for assuredly they who plead
thus against re-immersion for assuredly they who plead thus against
re-immersion never knew the truth. Immersion is not baptism, neither is
re-immersion re-baptism, if they can possibly understand the difference—which
one would suppose self-evident to the merest tyro. It is the candidate’s firm
assurance that the blood of Jesus Christ cleanses from all sin that he rose
again from the dead that makes his immersion in water baptism. If he does not
believe this—and he can only believe it on divine testimony contained in the
Scriptures—he is doubtless immersed, for that is a matter of fact; but he is
not baptized, for that is a matter of faith. Do not let me be misunderstood
here: no one can be baptized, if he have all the faith in the universe, unless
he is immersed in water; and one may be immersed and re-immersed fifty times,
but if he be destitute of faith, as the thousands of the immersed fanatics of
the Baptist denomination are, he is uncleansed, unsanctified, unreconciled,
unadopted, unsaved, and because he is unbaptized. Re-immersion therefore
ought to be repeated, in the case of such, provided always that they have that
assurance of which they were destitute at their first immersion. A re-immersion
upon said assurance is baptism to them only for the first time, and not a
re-baptism as some erroneously imagine. (John Thomas, letter to Alexander
Campbell, December 20, 1835, in In Search of a Biblical Faith: The Letters of
Dr. John Thomas to Alexander Campbell, 1833-47, ed. Reg Carr [Birmingham,
U.K.: The Testimony, 2022], 85-86), emphias added