Also I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? Then said I, Here am I; send me.
Whom shall I send, and who will go for us? The change of number indicates the Trinity (cf. Genesis 1:26; Genesis 11:7). Though not a sure argument for the doctrine, for the plural may in indicate merely majesty, it accords with that truth, proved elsewhere.
Whom ... who - implying that few would be willing to bear the self-denial which the delivering of such an unwelcome message to the Jews would require on the part of the messenger, (cf. 1 Chronicles 29:5, "who then is willing to consecrate his service this day unto the Lord?")
Here am I - prompt zeal, now that he has been specially qualified for it (Isaiah 6:7: cf. 1 Samuel 3:10-11; Acts 9:6).