Unstable as water. Figure of speech Simile. Compare Num_16:1, Num_16:2; Num_32:1.
water . . . thou. Figure of speech Ellipsis here (App-6. b). The word "unstable" = to flow down, and requires the Ellipsis to be filled up thus: "Flowing down as water [passes away, so] thou shalt not excel". What thus would pass away is set forth in Gen_49:3, and so it came to pass (1Ch_5:1).