Isaiah 19:23

There shall be a highway - A communication; that is, there shall be an alliance between Egypt and Assyria, as constituting parts of one empire, and as united in the service of the true God. The same figure of a “highway” is found in Isaiah 11:16 (see the note on that place). The truth was, that Alexander, by his conquests, subjected Assyria and Egypt, and they constituted parts of his empire, and were united under him. It was true, also, that there were large numbers of Jews in both these countries, and that they were united in the service of the true God. They worshipped him in those countries; and they met at Jerusalem at the great feasts, and thus Judah, Assyria, and Egypt, were united in his worship.

And the Assyrian shall come into Egypt - There shall be free and uninterrupted contact between the two nations, as parts of the same empire.

And the Egyptians shall serve with the Assyrians - In the same armies; under the same leader. This was the case under Alexander the Great. Or the word ‘serve’ may mean that they would serve God unitedly. So Lowth and Noyes render it.