[i]Prayer will singularly assist you in the delivery of your sermon:
in fact, nothing can so gloriously assist you to preach as descending fresh from the mount of communion with God to speak with men. None are so able to plead with men as those who have been wrestling with God on their behalf. It is said of Alleine, "He who poured out his very heart in prayer and preaching. His supplications and his exhortations were so affectionate, so full of holy zeal, life and vigour, that they quite overcame his hearers; he melted over them, so that he thawed and mollified, and sometimes dissolved the hardest hearts." There could have been none of this sacred dissolving of heart if his mind had not been previously exposed to the tropical rays of the Sun of Righteousness by private fellowship with the risen Lord. A truly pathetic delivery, in which there is no affectation, but much affection, can only be the offspring of prayer. There is no rhetoric like that of the heart, and no school for learning it but at the foot of the cross. It were better that you never learned a rule of human oratory, but were full of the power of heavenborn love, than that you should master Quintilian, Cicero, and Aristotle, and remain without the apostolic anointing.
Prayer may not make you eloquent after the human mode, but it will make you truly so, for you will speak out of the heart; and is not that the meaning of the word eloquence? It will bring fire from heaven upon your sacrifice, and thus prove it to be acceptable of the Lord.
Lectures To My Students
Ch. 4 - The Preacher's Private Prayer