God has never enjoined on human beings the duty of believing without evidence. He has never addressed us other than as rational beings, capable of discerning between truth and falsehood, and expected to do so on our own responsibility.
Revelation came not to supersede reason, or to set aside its deductions; but to enlighten its course, to expand its views, to enlarge its field of action, to dispel the earth-born mists that obscured its vision, to give it broader and more solid premises, on which to build its conclusions, and to prep its wings for a higher flight.
It never calls for the subjection of reason - the 'prostration' of the understanding, to its dictates. On the contrary, it is itself subjected to the decision of reason; and must abide the test. It must be received or rejected according to the dictates of our sober judgment on the evidence presented. And as with the evidence on which it rests, so with the doctrines it contains.
These too, are subjected to the test of reason. We believe them just in so far as we understand them; and no farther. The provinces of faith and reason are not distinct, the one beginning where the other ends. They cover the same ground.
It seems to us a mere identical proposition to state that what is not understood, cannot be believed. In this case no object is presented to the mind for it to receive or reject. What is not understood is to me no revelation. If a man say that he believes what he does not pretend either to explain or comprehend, he deceives himself. His faith is merely verbal and illusory.
Doubtless there may be many truths both in nature and in scripture, of which we are ignorant. But to us, so long as we remain ignorant of them, they are nothing - they are to us as though they did not exist.
We pretend not to comprehend the nature and perfections of the Divine Being, for example; but in so far as they are displayed, they are perfectly plain and intelligible - 'he that runs may read them.' And what is not displayed is no concern of ours.
My eye cannot penetrate the deep infinitude of the space that surrounds me; but within the verge of my own horizon I can see clearly, and move freely. Let it not be said that we exalt reason at the expense of revelation. We do but assign to each its appropriate sphere.
Reason, we must admit, was weak and inefficient by itself. And why? It lacked authority to still the clamor of the passions, that disturbed its operations. It lacked facts to render its conclusions certain.
Above all, it wanted sanctions to bind them on the conscience. All this revelation has supplied; and thus, it has completed the system of God's dispensations to humanity.
Those who vilify and degrade human reason; representing it as corrupt and debased; cautioning us continually against trusting to its guidance, and making it the test of a docile and humble spirit, and urging us to embrace doctrines from which reason recoils; do justice neither to reason, nor to scripture; neither to human beings, nor our Maker.
(Adapted from “Presumptive Arguments in Favor of Unitarianism" Jan. 1834, by Rev. Martin Luther Hurlbut)