(19–21) “He has let the two seas flow, meeting together. * Between them is a barrier which neither transgresses. * Which, then, of your Lord’s favors will you both deny?”

The two seas mean the fresh-water sea and the salt-water sea. The two meet, as fresh water flows into the salt water and they mingle and blend. Yet Allah Most High placed between them a barrier of land so that neither encroaches upon the other and benefit may be derived from each. They drink from the fresh water, as do their trees and crops. The salt water makes the air wholesome, and whales, fish, pearls, and coral form within it. It is also a stable expanse made serviceable for ships and vessels. Hence He said: