They were to flee because the Lord purposed to send His representative to plunder the nations for afflicting His people, the apple (lit. gate, the pupil, which is the most sensitive part) of His eye (cf. Matthew 25:31-4633; Psalm 17:8; Matthew 25:34-45; Acts 9:1; Acts 9:4-5). This would result in His glory. [source][source][source]
"This statement [1] anticipates the New Testament revelation of the Father sending the Son to glorify Him, both in His first advent ( John 17:4, cf. Isaiah 61:1-2; Luke 4:17-19) and in His second advent ( Isaiah 61:1-2)." [2][source]
"This will be fulfilled in the judgment of the Gentiles at Messiah"s Second Advent ( 1713449784_6)." [3][source]
The person whom the Lord would send as His representative ("Me") could not be Zechariah , in view of what the following verses say He would do. He must be Messiah, the only one with sufficient power and authority to fulfill what God predicted here. He would simply wave His hand over these nations in a menacing gesture and they would become plunder for the Israelites whom they had enslaved (cf. Esther 7:10; Isaiah 11:15; Isaiah 14:2; Isaiah 19:16; Galatians 6:7-8). Then God"s people would know that Yahweh of armies had sent this One (cf. Isaiah 61:3; John 17:4). This would be the sovereign Lord"s doing, so the Jews should rejoice, return to the land, and prepare. [source][source][source]