Baptist theologian John Gill (1697-1771) points out that preaching is work, “the work of the ministry” (Eph 4:13):

the ministry is a service, as the word imports, and not a sinecure; there is business to be done, and a great deal of it; enough to employ all the time and talents of ministers, and no room nor leisure to indulge to sleepiness, to laziness, and slothfulness: and it is a laborious work; the ministers of the gospel are not to be loiterers, but labourers in Christ’s vineyard; they labour in the word and doctrine, which requires much reading of the scriptures, frequent prayer, and constant meditation and study, in preparing for their work, which is a great weariness to the flesh; and much zeal, fervour, and affection in the performance of it, which is attended with much fatigue, and an expense of the animal spirits.” (Body of Practical Divinity, 927)