Tafsir of Ar-Rahman 55:19

"He let loose the two seas" means He released them and made them flow. It is derived from the expression "I let the animal loose in the pasture," meaning I let it roam therein. The meaning is that He released the salt sea and the fresh sea.

"Meeting [each other]" means they draw near to one another, and their surfaces touch, with no partition between them in the sight of the eye.

It has been said: He released the Persian Sea and the Roman Sea, which meet in the ocean, for they are two gulfs that branch out from it. This was narrated from Qatada. However, an objection was raised against it: it does not align with His saying, "One is fresh and sweet, and the other is salty and bitter," and the Quran explains itself. Based on this, it has been said: The clause "meeting [each other]" is a state of anticipation (a future-oriented state) if the intention is their release into the ocean; or the meaning is the unity of their origins if the intention is their release into it.