“As rivers pour into the sea, which stays full and unmoved, so the one whom all desires enter, yet who stays still, comes to peace.”

The sea takes in every river and stays the sea. The image describes a person whom wants and impressions still enter, in full flood, while something in them stays level and unmoved.

Peace in this verse is roomy. Nothing needs to be fenced out; it all pours in and finds a vastness that can hold it.