R.L. Dabney (1820-1898) was an American theologian whose book on Sacred Rhetoric (reprinted in 1999 under the title Evangelical Eloquence) is a fine guide to preaching. According to Dabney, the cardinal pre-requisites of the sermon are:-
1. Textual Fidelity. ‘The preacher is a herald. The first quality of the good herald is the faithful delivery of the very mind of his king.’ Textual fidelity not only ensures faithfulness to the mind of God, but also gives fruitfulness and variety of matter. ‘The steady contemplation of definite truth in its definite relaitons enriches the mind with instructive thoughts. If your powers are relieved of this labour by the permission to rove, they will remain barren and unawakened, and will run the narrow round of your familiar commonplaces.’
2. Unity. This does not mean sameness. It does not forbid variety, diversity, or even contrast, in the subordinate parts. It is the combination of the parts into one whole. Rhetorical units requires the speaker, firstly, to have one main subject, and, secondly, to make one definite impression on the hearer’s soul. ‘The proper image of rhetorical unity is not found in the star, which scatters its rays on every side from one point of light, to be absorbed and lost in the darkness of space, but in the lens, which collects many parallel or even dissentient rays into one burning focus.’ A sermon on ‘justification by faith’ would not have such unity; a sermon on ‘justification is by faith’ would.
3. Evangelical Tone. This is a ‘gracious character’, qualifying both the matter and the manner of the sermon. As to matter, this amounts to ‘preaching Christ’, making the Saviour central in the teaching. Evangelical tone also includes ‘unction’ – ‘that temperature of thought and elocution, which the Spirit of all grace sheds upon the heart possessed by the blessed truths of the gospel.’ It is a mixture of gravity and warmth.
4. Instructiveness. The instructive sermon ‘abounds in food for the understanding. It is full of thought, and richly informs the mind of the hearer.’ It is opposed to the commonplace, and also to the irrational. Although such a preacher will limit the content of his sermon to the circle of revealed truths, he must be a man of diligent study and ripe acquirements. ‘Religion is an intelligent concern, and deals with man as a reasoning creature. Sanctification is by the truth. To move men we must instruct.’
5. Movement. True eloquence does not result from a mere transmission of concepts, opinions, information; it is, rather, ‘the emission of the soul’s energy through speech’. If movement is of the essence of real eloquence, then its purpose is the same: to ‘to impel the hearers to some action of soul through the incitement of their own rational emotions’. Movement implies continuity, or sustained progress, we are not thinking of some isolated blow or shock. There must be progression in narrative, in argument, in persuasion. But movement has an emotional element too, and the direction will be from mental convictions to emotions. The preacher will avoid the mere repetition of ideas: legitimate amplification will involve progress, and be climactic. Avoid needless repetitions and digressions. The words themselves should be uttered with deliberate readiness. A discourse should be like a river: sometimes flowing more rapidly than at other times, but never stagnant.
6. Point. The thought must be incisive. In order to this there must be a chief truth, ‘distinctly apprehended by the speaker in its relation to the action of soul which he would excite’. And the whole discourse must be arranged so as to make this chief truth salient. An oration’s ‘point’ is like the prow of an old fighting ship, supported and strengthened by all the other timbers, whether directly or remotely, thus enabling it to be driven into the side of the adversary. The appropriate style for such a sermon individualises the hearer, addresses him in the second person, and prefers the special statement to the general and the concrete to the abstract. ‘Let the preacher cultivate that faith which makes the ruin and the rescue of sinners dread realities to him; let him share the constraining love of Christ in its power; let him feel a consuming zeal to save souls. Then he will not go into the pulpit aimless..he will have a definite and absorbing purpose, a message to deliver, and a result to effect, which he cannot leave unaccomplished without grief.’
7. Order. This includes both order (proper arrangement of the parts) and division (discriminating the parts). There is order everywhere in creation; everything follows the laws of nature. Order gives the difference between a pile of stone and timber and a house; between a collection of coloured pebbles and a mosaic; between a mob of men and an army; between chaos and creation. Order promotes recollection of the discourse by both preacher and hearer. Just as a series of words forming a sentence is much easier to recall than a random series of words, so a series of connected thoughts is more readily remembered than a series of random thoughts. Order also lends beauty, and ‘it is a noble thing to make the truth beautiful!’ Order in preaching promotes accuracy and analysis, just as in botany the careful classification of a mass of plants does. Order promotes fruitfulness of the mind, because seeing the relationship between ideas often produces new ideas. Systematic thinking (that is to say, orderly thinking) brings to mind thoughts that had been retained only in our unconscious memories.
Sacred Rhetoric, 105-136.