Quoting Commentary for Zechariah 6:1

ויסר מעלינו את הנחש “so that He will remove the snake (plague of) from us.” Actually, we would have expected the word הנחשים, “the snakes” (pl.), instead of the word הנחש, “snake” (sing.). The reason the Torah uses the singular is to allude to the lethal power of the snake, serpent, mentioned earlier. The Torah refers to the spiritual representative of the snakes whose residence is in the desert. When the Jewish people said מעלינו, instead of ממנו, they meant “the one who is above us,” instead of merely “away from us.” We find a similar expression in Numbers 14,9 where Calev described that the protective force of the Canaanites had already been withdrawn from them as: סר צלם מעליהם, “their protective shadow has departed from above them.” This will also enable you to understand a verse in Zecharyah 6,1 וההרים הרי נחשת, “and the mountains are mountains made of copper” [a comment which appears irrelevant at first glance. Ed.]. The word נחשת is understood as derived from השחתה, “destruction.” Although the mountains mentioned by the prophet are destructible, the four chariots representing the glory of the Lord mentioned in that same verse are indestructible (based on Maimonides Moreh Nevuchim section two 10th chapter). It is a reference to the “great mountain” which features in the vision of Zerubabel as an insurmountable obstacle but which G’d promises will be reduced to level ground (vision of Yehoshua High Priest, Zecharyah 4,7)