Whom shall I send? And who will go for us?

It's amazing how the Words of God in a single verse can make such vast difference and mean so much. Was reading up "My Utmost For His Highest" and today's reading was titled "Called by God".

I've always had this understanding that in being called by God, you are SPECIFICALLY called by God; to help people, to lead a CG, to influence the world, etc. However, that is not it. This is what Isaiah 6:8 says:

Then I heard the voice of the Lord saying, "Whom shall I send? And who will go for us?" And I said, "Here am I. Send me!"

Intriguingly, God wasn't talking directly to Isaiah. For he said, "who will go for us?" It was Isaiah, whose spiritual ears were sharp, who heard God's calling and responded to it.

Though I'm quite certain that God had meant that calling for Isaiah, but it was Isaiah who heard God's voice that he took up this calling that God gave. God is always constantly calling out for us, all of us. But the question is, who can hear His call?