He sends down water from the heavens, then the valleys flow according to their measure, and the torrent bears along the swelling foam, and from what they melt in the fire for the sake of [making] ornaments or apparatus arises a scum like it; thus does Allah compare truth and falsehood; then as for the scum, it passes away as a worthless thing; and as for that which profits the people, it remains in the earth; thus does Allah set forth parables (13:17).

In his discourse about the presence of ambiguous verses in the Qur’an (Eng Vol. 5), Allamah Tabataba’i quotes the above verse which is the Qur’anic parable of truth and falsehood. He says that there is no difference between God’s actions and His speech because they are both meant for truth. However, both His actions and speech may be accompanied by some unintended elements or things. The unintended things temporarily cover and hide the intended truth. This is evident from the clause, and the torrent bears along the swelling foam. But they soon pass away and the truth remains to benefit the people: then as for the scum, it passes away as a worthless thing. In other words, another truth (or, a decisive verse) makes the scum (or, the ambiguity) to pass away.

Following, is the gist of the above discourse:  

Rather strikingly, in the above parable, the Divine realities and spiritual knowledge are likened to the water which God sends down from the heavens. Originally, the water is pure and not hindered with any other condition. But, when the rain hits the earth, the water starts to flow and take the shape of a watercourse—a wide river, a narrow stream and so on. These shapes and measures are established facts, they are not imaginary things and in this respect they resemble the benefits of the rules of the shariah.

Those rules, in the course of their flow, are often accompanied by a swelling foam that appears for a time being and then disappears. An example may be given of an abrogated verse; in the nature of thing it should have remained in force permanently, but another verse comes along, abrogates it, and puts another rule in its place. This development also is an established fact; it does not matter whether this religious reality has been clothed with words.

The spiritual realities and metaphysical ideas, inasmuch as they are placed in the containers of the words, take the shape of those containers; and are fettered with the demands of the word and the language—though originally they had no such limitation or restraint. These words are true and fact, because they were chosen by the truthful Speaker to convey His message. Yet they are like a similitude that represents the real meaning—the meaning that is unfettered by the words, unencumbered by the shapes of these containers. Therefore, the words pass through the minds of the hearers and unintended meanings surround them and ride high above them. It happens because the minds look at the words in the light of their previously acquired ideas. This mostly happens about those realities that are not familiar to common minds, like the spiritual facts, the real reason for which a certain rule was ordained and so on. But so far as the rules themselves are concerned, there occurs no change, because invariably they always talk about what is within the sphere of man’s own activities, and is, therefore, familiar to him.

The above discourse shows that ambiguous verses are ambiguous because they contain the spiritual realities and not the rules of religion and shariah.

Reference: Al-Mizan Eng. Vol. 5 (Pub. by WOFIS)