And God created the big sea creatures, and every living, creeping soul that the waters caused to creep out, in all their kinds, and every bird on the wing, of every kind; and God saw that it was good. — Genesis 1:21
Fish symbolize facts, as already stated [Section 40]. In this instance they symbolize facts animated by faith that is received from the Lord, which therefore possess vitality. Big sea creatures symbolize general categories of facts, from which come subcategories. (Not one thing exists anywhere in the world that does not belong to some general category. The category allows the particular item to come into being and continue in existence.)
The prophets mention sea monsters or whales a number of times, and when they do, these symbolize general categories of facts. Pharaoh, king of Egypt, representing human wisdom or understanding (that is, factual information in general), is called a large sea creature, as in Ezekiel:
Here, now, I am against you, Pharaoh, king of Egypt, you great sea creature, lying in the middle of your rivers, who has said, “The river is mine, and I have made myself.” (Ezekiel 29:3)
Another:
Raise a lamentation over Pharaoh, king of Egypt; and you are to tell him, “But you are like a monster in the seas; and you have emerged among your rivers and churned the waters with your feet.” (Ezekiel 32:2)
This image symbolizes those who want to use facts (meaning they want to use their own powers) to initiate themselves into religious mysteries. In Isaiah:
On that day Jehovah, with his steely and great and mighty sword, will exact punishment on Leviathan the stretched-out serpent and on Leviathan the coiled serpent; and he will kill the monsters that are in the sea. (Isaiah 27:1)
Killing the monsters that are in the sea means leaving such people without awareness even of general facts. In Jeremiah:
Nebuchadnezzar, king of Babylon, has devoured me, has churned me up; he has rendered me an empty container, like a sea monster he has swallowed me down, filled his belly with the savors of me, hurled me out. (Jeremiah 51:34)
In other words, “Nebuchadnezzar” has swallowed up all religious knowledge (the “savors”) as the sea monster did to Jonah. In Jonah’s case the monster stood for people who possess the broad outlines of this knowledge in the form of facts and who wolf them down.
from Secrets of Heaven, Volume 1, Section 42
Secrets of Heaven 