This seems a new Sermon of the Prophet's, opening at this Chapter. The stile is as usual in the prophetic way. Not only the people are called upon, but the inanimate part of the creation, to be witness of Israel's stupidity. See Isaiah 1:2, etc.
Related Commentaries of Micah 6:1
Micah 6:1-2
1 Hear ye now what the LORD saith; Arise, contend thou before the mountains, and let the hills hear thy voice.
2 Hear ye, O mountains, the LORD'S controversy, and ye strong foundations of the earth: for the LORD hath a controversy with his people, and he will plead with Israel.