The Children of Israel are fleeing slavery in Egypt. The Red Sea is a barrier across their path to Sinai, and Pharoah and his army are in pursuit. A miracle saves them - the waters are rolled back, and they cross on dry land. What does this story mean, in the internal sense?

This whole story, from Exodus 14:5-28, is explained in the work "Arcana Coelestia", starting from section 8141 and extending to section 8232.

In this brief explanation, let's focus just the part of the story in verses Exodus 14:19-25. Jehovah, represented in the pillar of cloud and fire, leads the Children of Israel to the Red Sea. He separates them from the Egyptians, and then - through the night - causes a strong east wind to divide the waters of the Read Sea, so that the Israelites can cross on dry land. In the morning, the camp of the Egyptians is troubled, and their chariots lose wheels, and drive heavily.

Here's what the story means, (as drawn from sections 8192-5 of Arcana Coelestia):

As we follow the leading of the Lord, we open our minds to be rearranged by Divine Truth. We begin to make progress towards having more true ideas, and loves for doing good things.

While this is happening, we are protected, by the Lord, from the influx of false ideas that stem from evil loves, and our newfound loves for good - for God and our neighbors - are protected, too.

God stands between our false ideas, represented here by Egypt, and the truths that are becoming clearer, springing from good loves, represented here by Israel. If we have the "Egypt" mindset, our evils, and the false ideas that arise from them, keep us in darkness. If we're trying to follow God's leading, the night is lit up for us.

Our warring mindsets are separated; they don't communicate.

When we are in states of obscurity, God continues to operate in our minds, increasing the strength of our true ideas and dispersing our false ones. Truths are separated from falsities.

As we trust in the Lord, we are able to cross the Red Sea spiritually - to get through the hellishness that is blocking our passage, and be protected so that we are not overwhelmed by falsity. Even so, we still get attacked by the Egyptians - Pharoah, his host, chariots and horsement. These stand for facts that come from a twisted understanding of what's real, true, and important, and doctrines that reinforce false ideas, and human reasoning from our merely natural minds - they come after the new truths in our spiritual minds.

God's love and wisdom flows into our minds, and "trouble the camp of the Egyptians". The evil loves and false ideas recoil from this influx. The false ideas lose their power. They are separated from our true ideas and good loves.

This happens when we open our minds to the Lord's leading; it's Divine power, not ours, that really fights and wins the battle.