“a speck of dust on a balance.” The “balance” is what merchants used to buy and sell. The dust would never even affect a biblical balance—they were too crude. See commentary on Proverbs 11:1.

“he lifts up the islands.” The “islands” are at the far reaches of the known world at that time, hence they are used to refer to things at the ends of the earth (cp. John Oswalt, NICOT, The Book of Isaiah: Chapters 40-66).