There is quite a segue in Psalm 46, from :3, where it says the “waters roar and foam” to :4, which contains the peaceful, “there is a river whose streams make glad the city of God.” The waters are described as going from tumultuous to peaceful – upon the contemplation of the “very present help” of God which is referenced throughout the Psalm:

— :1 “God is our refuge and strength, a very present help in trouble.”
— :5 “God will help her when morning dawns.”
— :7 “The Lord of hosts is with us.”
— :10 “Cease striving and know that I am God” – and so on.

This knowledge that God was with him soothed the heart of the Psalmist, as pictured in the changing description of the waters from “roaring and foaming” to peaceful “streams (which) make glad.” Even today, when we remember that God is with us, and contemplate His “very present help” which is described in this Psalm, we can experience that same transition — from tumult to peace — in our own hearts.