Jesus is the "salvation of God" (yeshua) within us and the sea is a metaphore for the state of our subconscious thoughts, out of which spring good and evil. The "salvation of God" is able to rise above the turbulent seas of that mind and still the sea. When it becomes the crystal sea then is perfectly still and can know God because it is a vessel that can reflects his thoughts.
The scriptures state it plainly: "Be still and know that I am God". JB