Charles Ellicott Commentary Isaiah 60:5

"Then thou shalt see and be radiant, and thy heart shall thrill and be enlarged; because the abundance of the sea shall be turned unto thee, the wealth of the nations shall come unto thee." — Isaiah 60:5 (ASV)

Then you will see. — A variant reading adopted by many commentators gives you will fear.

Your heart will fear ... — Literally, it will throb with an awe-stricken joy at the marvelous prosperity, but that throb of awe is followed by the expansion of ecstatic joy.

The abundance of the sea — that is, the riches of the Western isles, with which the new Jerusalem was to be filled, as Tyre and Sidon had been in ancient times (Ezekiel 27:1–25).