In Genesis 2:14 and Psalms 80:9, 10, the Euphrates symbolizes secular knowledge — facts — and the sensory impressions on which facts are based. (Secrets of Heaven 120)

120. Like Egypt, the Euphrates too means knowledge or facts, and also sensory evidence from which facts are obtained. This is clear from the Word in the Prophets, as in Micah, She, my enemy, said, Where is Jehovah your God? A day on which He will build your walls. On that day what has been determined will be absent afar off. That day also He will come to you from Asshur, and to the cities of Egypt and to the River (the Euphrates) Micah 7:10-12.

The Prophets spoke in this way when referring to the coming of the Lord, who was going to regenerate man so that he would become as a celestial man. In Jeremiah,

What have you to do with the way to Egypt, to drink the waters of Shihor? And what have you to do with the way to Asshur, to drink the waters of the River (the Euphrates)? Jeremiah 2:18.

Here similarly 'Egypt' and 'the Euphrates' stand for facts, and 'Asshur' for reasonings based on them. In David,

You did cause a vine to journey out of Egypt. You did cast out the nations, You did plant it. You did send out its shoots even to the sea, and its little branches to the River (the Euphrates) Psalms 80:8, 11.

Here too 'the river Euphrates' stands for sensory evidence and factual knowledge. Indeed the Euphrates was the boundary to Israel's territories in the direction of Asshur, just as factual knowledge in the memory is the boundary of intelligence and wisdom of the spiritual and celestial man. The same is meant by these words addressed to Abraham,

To your seed I will give this land, from the river of Egypt even to the great river, the river Euphrates. Genesis 15:18.

Both of these two boundaries have the same meaning.