"They will know that I am Lord" is the resounding words of God to the prophet. He repeats them over and over with a clarity you can't miss. God wants his people, all people to know that HE is Lord.
When men declare that evidence for God is minimal at best God declares that one day all men will know that he is Lord of heaven and earth. It's his desire for each one of us to know him.
I've often heard the argument, "but what about the African who has never heard?" God will make sure he hears. Don't worry about him, but realize you have heard...now what are you going to do?
They will know that I am Lord.
One day everyone will know that the God of the bible is Lord of heaven and earth, creator of the earth and heavens, savior of whoever will come. One day we all will know.