The Christian preacher is not the successor of the Greek orator, but of the Hebrew prophet.
The orator comes with but an inspiration, the prophet comes with a revelation. In so far as the preacher and prophet had an analogue in Greece it was the dramatist, with his urgent sense of life’s guilty tragedy, its inevitable ethic, its unseen moral powers, and their atoning purifying note. Moreover, where you have the passion for oratory you are not unlikely to have an impaired style and standard of preaching.
Where your object is to secure your audience, rather than your Gospel, preaching is sure to suffer. . . . It is one thing to have to rouse or persuade people to do something, to put themselves into something; it is another to have to induce them to trust somebody and renounce themselves for him. The one is the political region of work, the other is the religious region of faith. And wherever a people is swallowed up in politics, the preacher is apt to be neglected, unless he imperil his preaching by adjusting himself to political or social methods of address.
The orator, speaking generally, has for his business to make real and urgent the present world and its crises; the preacher a world unseen, and the whole crisis of the two worlds. The present world of the orator may be the world of action, or of art. He may speak of affairs, of nature, or of imagination. In the pulpit he may be what is called a practical preacher, or a poet-preacher.
But the only business of the apostolic preacher is to make men practically realize a world unseen and spiritual; he has to rouse them not against a common enemy but against their common selves; not against natural obstacles but against spiritual foes; and he has to call out not natural resources but supernatural aids. Indeed, he has to tell men that their natural resources are so inadequate for the last purposes of life and its worst foes that they need from the supernatural much more than aid.
They need deliverance, not a helper merely, but a Saviour.
The orator stirs men to rally, the preacher invites them to be redeemed.
Demosthenes fires his audience to attack Philip straightaway; Paul stirs them to die and rise with Christ.
The orator, at most, may urge men to love their brother, the preacher beseeches them first to be reconciled to their Father.
With preaching Christianity stands or falls because it is the declaration of a Gospel. Nay more—far more—it is the Gospel prolonging and declaring itself.
P.T. Forsyth, from Positive Preaching and Modern Mind, pp. 3-5 (emphasis & paragraph breaks mine)