The Lord God will help me - (See Isaiah 50:7). In the Hebrew this is, ‘The Lord Jehovah,’ as it is in Isaiah 50:7 also, and these are among the places where our translators have improperly rendered the word יהוה yehovâh (Jehovah) by the word ‘God.’
Who is he that shall condemn me? - If Yahweh is my advocate and friend, my cause must be right. Similar language is used by the apostle Paul: ‘If God be for us, who can be against us?’ Romans 8:31; and in Psalms 118:6 :
Jehovah is on my side; I will not fear:
What can man do unto me?
They all shall wax old - All my enemies shall pass away, as a garment is worn out and cast aside. The idea is, that the Messiah would survive all their attacks; his cause, his truth and his reputation would live, while all the power, the influence, the reputation of his adversaries, would vanish as a garment that is worn out and then thrown away. The same image respecting his enemies is used again in Isaiah 51:8.
The moth shall eat them up - The moth is a well known insect attached particularly to woolen clothes, and which soon consumes them (see the note at Job 4:19). In eastern countries, where wealth consisted much in changes of raiment, the depredations of the moth would be particularly to be feared, and hence, it is frequently referred to in the Bible. The sense here is, that the adversaries of the Messiah would be wholly destroyed.