Isaiah hears the call of the Lord for a messenger, and volunteers for the assignment. His call and response is eerily similar to an event in the pre-mortal life:
Abr. 3:27
27 And the Lord said: Whom shall I send? And one answered like unto the Son of Man: Here am I, send me. And another answered and said: Here am I, send me. And the Lord said: I will send the first.
Rather than presume that God doesn’t know who is special messengers will be, it is important to see the wording in these calls as an affirmation of the principle of agency. God so fully respects and adheres to agency that the call comes not in emphatic command, but rather in request. The language of the call and acceptance is witness to the willing service of the prophet.