Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal?
Richard Baxter, The Reformed Pastor (1830 ed.), p. 223:
My second particular exhortation is this: Content not yourselves to have the main work of grace, but be also very careful that your graces be kept in life and action, and that you preach to yourselves the sermons that you study, before you preach them to others.
Arthur Stephen Hoyt, The Work of Preaching (1905), p. 97:
You must preach to yourself before you can preach to others.
Charles H. Spurgeon, "Sermon X: Declension From First Love," in Sermons Preached and Revised by the Rev. C.H. Spurgeon, p. 174:
Now preacher, preach honestly, and preach at thyself.
Iain Murray, Dr. Lloyd-Jones and Authority in Preaching:
The preacher must know the power of the message he is bringing to others. When DMLJ was 25 and at the cross-roads of his life, he became engaged to Bethan Philips, and she became conscious that her future husband was considering becoming a preacher. She was very concerned because she had never heard him preach. At that point a letter came from a missionary society inviting them to become medical missionaries in India. She was challenged by this invitation but DMLJ had no interest at all. Bethan said to him, "But how do you know that you can preach?" "I know I can preach to myself" he replied. He knew the power of the truth in his own heart.
George Herbert, A Priest to the Temple, or, A Country Parson:
CHAP. XXXIII. The Parson's Library.
THe Countrey Parson's Library is a holy Life: for besides the blessing that that brings upon it, there being a promise, that if the Kingdome of God be first sought, all other things shall be added, even it selfe is a Sermon. For the temptations with which a good man is beset, and the ways which he used to overcome them, being told to another, whether in private conference, or in the Church, are a Sermon. Hee that hath considered how to carry himself at table about his appetite, if he tell this to another, preacheth; and much more feelingly, and judiciously, then he writes his rules of temperance out of bookes. So that the Parson having studied, and mastered all his lusts and affections within, and the whole Army of Temptations without, hath ever so many sermons ready penn'd, as he hath victories. And it fares in this as it doth in Physick: He that hath been sick of a Consumption, and knows what recovered him, is a Physitian so far as he meetes with the same disease, and temper; and can much better, and particularly do it, then he that is generally learned, and was never sick. And if the same person had been sick of all diseases, and were recovered of all by things that he knew; there were no such Physician as he, both for skill and tendernesse. Just so it is in Divinity, and that not without manifest reason: for though the temptations may be diverse in divers Christians, yet the victory is alike in all, being by the self-same Spirit. Neither is this true onely in the military state of a Christian life, but even in the peaceable also; when the servant of God, freed for a while from temptation, in a quiet sweetnesse seeks how to please his God. Thus the Parson considering that repentance is the great vertue of the Gospel, and one of the first steps of pleasing God, having for his owne use examined the nature of it, is able to explaine it after to others. And particularly, having doubted sometimes, whether his repentance were true, or at least in that degree it ought to be, since he found himselfe sometimes to weepe more for the losse of some temporall things, then for offending God, he came at length to this resolution, that repentance is an act of the mind, not of the Body, even as the Originall signifies; and that the chiefe thing, which God in Scriptures requires, is the heart, and the spirit, and to worship him in truth, and spirit. Wherefore in case a Christian endeavour to weep, and cannot, since we are not Masters of our bodies, this sufficeth. And consequently he found, that the essence of repentance, that it may be alike in all Gods children (which as concerning weeping it cannot be, some being of a more melting temper then others) consisteth in a true detestation of the soul, abhorring, and renouncing sin, and turning unto God in truth of heart, and newnesse of life: Which acts of repentance are and must be found in all Gods servants: Not that weeping is not usefull, where it can be, that so the body may joyn in the grief, as it did in the sin; but that, so the other acts be, that is not necessary: so that he as truly repents, who performes the other acts of repentance, when he cannot more, as he that weeps a floud of tears. This Instruction and comfort the Parson getting for himself, when he tels it to others, becomes a Sermon. The like he doth in other Christian vertues, as of Faith, and Love, and the Cases of Conscience belonging thereto, wherein (as Saint Paul implyes that he ought, Romans 2.) hee first preacheth to himselfe, and then to others.