Charles Ellicott Commentary Isaiah 60:16

"Thou shalt also suck the milk of the nations, and shalt suck the breast of kings; and thou shalt know that I, Jehovah, am thy Saviour, and thy Redeemer, the Mighty One of Jacob." — Isaiah 60:16 (ASV)

You shall also suck the milk of the Gentiles ... —The metaphor is bold, but the prophet had already presented it in a less startling form in Isaiah 49:23. What is meant in either case is that the new Jerusalem shall be supported by the offerings of the Gentiles.