Having found true eloquence to be the soul's virtuous energy exerted through speech, I would remind you that the sermon is a peculiar species of eloquence. Like all other eloquence, it aims always to produce a definite, practical volition in the hearer. This aim is, in the best sense, a worthy one; for the acts it evokes are the spiritual. But its peculiarity is chiefly this, that it applies to the will, the authority of God, the only Lord of the conscience. This alone, I repeat, makes the gospel discourse. Other orators bring to bear upon the understandings of their hearers the force of human testimony and natural reason; they apply to their hearts legitimate secular and moral inducements. The preacher relies alone upon evangelical inducements, and refers every conviction of the reason ultimately to God's testimony. I elaborate this all-important distinction carefully; perhaps my reasons for it are difficult to grasp, because of their simplicity. The end, I repeat, of every oration is to make men do. But the things which the sermon would make men do, are only the things of God. Therefore it must apply to them the authority of God. If your discourse urges the hearer merely with excellent reasons and inducements, natural, ethical, social, legal, political, self-interested, philanthropic, if it does not end by bringing their wills under the direct grasp of a "thus saith the Lord,' it is not a sermon; it has degenerated into a speech.
The emboldened statement is the focus of my interest here, for it implies a presuppositional approach to preaching, namely, that all reasons or testimonies presented to the hearer as support for a claim must ultimately be annexed to or derivative of Scriptural propositions. I am not sure that Dabney has his mind on this point in particular, or that he even recognizes it, for it is possible given the rest of the quote that he separates secular from sacred thinking. However, I suspect that Dabney would acknowledge that even arguments "natural, ethical, social, legal, etc." must be grounded upon Revelation in order to be sustainable for Christian belief and practice, or indeed all sound belief and practice. Whatever the case, the quote is a superb reminder to preachers that whatever arguments or examples they produce in their sermons, they ought to derive them, clothe them, and otherwise immerse them in Biblical presuppositions--and whenever possible, do so by using the Bible's own terms and language.