The Holy Book has also resorted to the form of an oath in another place when describing the need and truth of revelation by appealing to the laws of Nature:

"By the cloud giving rain, and the earthng (with herbage)! Surely it is a decisive word, and it is not a joke" (11-14)

Here, the Almighty calls attention to His manifest law in the form of an oath as testimony for the truth of the revelation of the Quran. It is plainly seen in the laws of Nature that rain comes down from heaven in time of need. The greenness and verdure of the earth depend upon heavenly rain. If it ceases for a time, the water in the upper strata of the earth gradually dries up. Thus we perceive that there is a connection between the heavenly and the earthly waters. Revelation stands in the same relation to human reason as heavenly water does to the earthly water. As with the cessation of heavenly water earthly water begins gradually to dry up, so also is the case with human reason which, without the heavenly revelation, loses its purity and strength. When, therefore, a long period of time elapses without witnessing the appearance of any inspired one of God, it is but natural that reason, like earthly water, should become noxious and impure.

As an illustration of this principle, we may cast a glance at the pre-Islamic period. Before Prophet Muhammad had appeared, darkness prevailed everywhere. About six hundred years had passed since the advent of Jesus Christ, and during this long interval no inspired one of God had made his appearance. The whole world witnessed to a falling off from purity and virtue, and corrupt ideas prevailed widely. This was due to no other factor but to the discontinuance of revelation. Reason, and not revelation, held sway and, on account of its imperfection and corruption, led people astray. The earthly water of human reason dried up because the heavenly water of inspiration had not come down upon earth for such a long time.

The Almighty directs the attention of men to His law that the earth's bringing forth of vegetation and verdure depends upon heavenly rain. This manifest law points to the secret law relating to revelation. Reason alone cannot be trusted, for its own existence is liable to decay if revelation does not afford it nourishment. When an inspired one of God appears upon the earth, his benevolence extends to all, and human reason is brightened and sharpened to a marked degree. There is a general search for truth and an animation and activity of all the dormant faculties is noticeable.