Charles J. Brown, The Ministry, pp. 28-29:
ii. But now, in the second place, I believe that one great source of the undue length of our public prayers lies in the inadequate measure of attention given among us to the whole subject, and, more specifically, the want of due forethought, premeditation, before the pulpit has been entered. Let me not be misunderstood. I am no advocate for the writing out of prayers and committing them to memory, and should greatly deprecate such a method. It is, however, a mere vulgar and groundless notion that there is no medium between this and a minister's entering his pulpit wholly at sea as to the prayers he is about to offer. It is but a fancy that free prayer is all one with wholly unpremeditated prayer. Assuredly, the Westminster divines entertained no such opinion; for if you examine the Directory for Public Worship you shall find that, while they give no forms of prayer, they give very full materials after the tenor of which the minister is to pray.
What I plead for, and would press very earnestly, is the marking out in the mind of some leading line of thought and petition not to tie the minister down, but rather to set him more free. Only think what the case is: a pastor leading the devotions of the same people twice every Sabbath, from week to week - during a long course of years, it may be. In the absence of serious forethought it is almost impossible but that one of two results should follow; either he must slide gradually into a form of his own, a repetition substantially of the same things Sabbath after Sabbath (to which, would not a good liturgy be preferable?) or else, in trying to avoid this, he must wander up and down, as some ship at sea without compass or rudder, at the mercy of every wind that blows. There is one blessed wind, at least, he shall be little likely thus to catch, even the gales longed for in those words of the Song of Solomon, 'Awake, O north wind; and come, thou south; blow upon my garden, that the spices thereof may flow out' (Song of Sol. 4:16). Oh, I think if these gales are to be found, the soul must be free, the whole exercise must be spontaneous and unconstrained.
And observe that, though you may have marked out a certain line of thought and petition in your mind, you are nowise tied down to follow it, but may vary it endlessly, according as circumstances, under the adorable Spirit of grace, may suggest. It may only be added here that I include in forethought all earnest desires after a frame of spirit suitable for public prayer, before entering the pulpit. The whole subject, in short, must come to occupy a larger place in our attention and esteem.