The following is an excerpt from the book, A Brief Treatise on Prayer by Robert Milligan. It was the first of five points he discussed about the advantages of secret prayer (Chapter II).
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The first of these is the cultivation of our own spiritual nature. If it is a law of the human constitution that all its powers and susceptibilities are developed and strengthened by exercise, then what can be more beneficial than the devotions of the closet? There is no other place beneath the heavens that is so favorable for the legitimate exercise of our moral faculties. Even in the religious assembly, the attention is often arrested and the heart made to wander by some improper display of the lusts of the flesh, the lusts of the eye, and the pride of life. But from the closet all such evil influences are excluded. There is no motive to deceive, or to make a vain display of our persons, our dress, and our good works. But there the mind turns in upon itself. There the conscience is awakened; there we see ourselves in the light of heaven. And there, under the deep, solemn conviction that we are on holy ground, and that the eye of God is upon us, we are almost compelled to be humble, to repent of our sins, to forgive our enemies, to sympathize with the afflicted, to adore our Creator, to love our Redeemer, and to exercise all the powers of our souls in harmony with the will of God.
An hour in the closet may, therefore, do more to rectify and strengthen our religious impressions and moral faculties than many days of ordinary service in the public congregation. And hence our Savior says to every disciple, “When thou prayest, enter into thy closet, and when thou hast shut the door, pray to thy Father who is in secret; and thy Father who seeth in secret, will reward thee openly.”