Israel and Judah had been put away and cast out for their iniquity, and the heavens lamented (Isaiah 50:1-3). 

YHWH gave Isaiah instruction to sustain the weary with prophetic exhortation.  Isaiah was struck and beaten, shamed and spat upon.  Yet YHWH would be his help, and he resolutely endured suffering without being ashamed. 

God would justify and stand with him; who could fight with him?  His enemies would be destroyed.