Since there is no verb in this phrase, it may be necessary in your language to supply one. Alternate translation: "You will not succeed by might nor by power" (See: [[rc://en/ta/man/jit/figs-explicit]])
Possible meanings are 1) that the words "might" and "power" mean basically the same thing and emphasize the greatness of Zerubbabel's strength or 2) that the word "might" refers to military strength and the word "power" refers to Zerubbabel's physical ability. Alternate translation: "Certainly not by your own strength" or "Not by military strength nor by your own power" (See: [[rc://en/ta/man/jit/figs-doublet]])