

Perhaps we may assume that Jesus knew as much as the Austrian did about saving people. But the thing which this fellow had overlooked, my friend, was that he had a predecessor in the reformation business, called Jesus Christ. He tried to impose his reformation by the sword, and plunged the civilized world into misery and chaos. There was just such a man when I was young-an Austrian who invented a new way of life and convinced himself that he was the chap to make it work.

Here, he speaks about Hitler in a way Wart might understand: One of the reasons he's absentminded is that he's always confused about time, since he's going through it in a different manner. Although Merlyn is powerful, he is also kind and a little absentminded. Arthur’s creation of the Round Table and a more civilized England is largely due to Merlyn’s influence. Merlyn - A magician who has already lived the future, so he knows what is going to happen next. Maybe someone else will find an earlier use. I can find uses of the phrase after the book but not before it. Some people have used once and future to indicate enduring or perpetual. It will not happen for hundreds of years, but both of us are to come back. I will tell you something else, King, which may be a surprise for you.

However, in the Book, Merlin does acknowledge that both he and Arthur will come again (a nod to Arthurian legend): That is the only famous use of the once and future that I know of, and as it is a well known book, any other use, especially in fantasy, would be referencing that title. In that way, he is, to Merlin (and Wart), both the once and future king. When he finally takes charge of Wart (Arthur), Wart is only a boy, who Merlin trains to be a King in Arthur's future. Merlin knows Wart's future very well, and also knows his own. White's book of that title about Arthur (if I remember correctly), Merlin, who plays a very prominent role in the book (perhaps more so than even Arthur, at least in the Sword and the Stone book), is traveling through time backwards, so to Merlin, Arthur already was king (Merlin complains about life in the 20th c).
