Jamieson, Fausset and Brown on Numbers 23:10

10. Who can count the dust of Jacob?--an Oriental hyperbole for a very populous nation, as Jacob's posterity was promised to be (Ge 13:16; 28:14).

the number of the fourth part of Israel--that is, the camp consisted of four divisions; every one of these parts was formidable in numbers.

Let me die the death of the righteous--Hebrew, "of Jeshurun"; or, the Israelites. The meaning is: they are a people happy, above all others, not only in life, but at death, from their knowledge of the true God, and their hope through His grace. Balaam is a representative of a large class in the world, who express a wish for the blessedness which Christ has promised to His people but are averse to imitate the mind that was in Him.