תהלים, פרק ק״ד, פסוק ט׳

Divine control over the forces of nature guarantees the survival of life on dry land by maintaining a permanent barrier that prevents the oceans from flooding the world. The sand on the shore serves as this natural border, acting as a line that the waters cannot cross [רש״י, רד״ק, מצודת דוד]. Establishing this boundary is a profound miracle and a direct intervention in the laws of nature. While water naturally flows from a higher place to a lower one, during the initial gathering of the oceans, the waters piled up like a high wall. God actively prevents the waves from crossing the sand and spilling onto the land, even though the land is considered higher than the sea [רד״ק].

The primary approach among commentators traces this ongoing protection back to the beginning of Creation. Initially, water completely covered the earth. By God's will, wind pushed the waters back to expose the dry land. A divine promise ensures that the oceans will remain in their fixed locations forever, never returning to engulf the planet as they did at the dawn of time [אבן עזרא, מצודת דוד, מלבי״ם, המאירי]. The ultimate purpose of this firm boundary is to protect all living creatures on land from destruction [רד״ק, המאירי]. In contrast to the view focused on Creation, another perspective links this boundary to specific historical events where the waters breached their limits. According to this approach, the initial restriction of the sea refers to a flood that punished the world during the generation of Enosh, while the guarantee that the waters will never again cover the earth points to the great Flood. Following those events, God firmly established the earth so that it would never falter [אלשיך].

As part of His careful supervision over the well-being of the world, God designed the waters to perfectly sustain life. Fresh water was left throughout the dry land to provide for human needs, while the massive bodies of ocean water were specifically made salty. Without this saltiness, such an enormous amount of water sitting in one place without flowing would rot, creating a terrible smell that would ruin the air of the entire world [המאירי].