The Hebrew that cannot be utter? Failed to understand the logic

If that could not be uttered, how could you know that is Hebrew? If you knew, you naturally uttered it in your heart; if so, why were still alive to speak to us?

Context:

The other phenomenon is the quite appalling nature of this Man's theological remarks. You all know
what I mean, and I want rather to stress the point that the appalling claim which this Man seems to be
making is not merely made at one moment of His career. There is, of course, the one moment which
led to His execution. The moment at which the High Priest said to Him, "Who are you?" "I am the
Anointed, the Son of the uncreated God, and you shallsee Me appearing at the end of all history as
the judge of the Universe". But that claim, in fact, does not rest on this one dramatic moment. When
you look into His conversation you will find this sort ofclaim running through the whole thing. For
instance, He went about saying to people, "I forgive your sins". Now it is quite natural for a man to
forgive something you do to him. Thus if somebody cheats me out of five pounds it is quite possible
and reasonable for me to say, "Well, I forgive you, we will say no more about it". What on earth would
you say if somebody had done you out of five pounds and I said, "That is all right, I forgive him"?
Sometimes the statements put forward the assumption that He, the Speaker, is completely without sin
or fault. This is always the attitude. "You, to whom Iam talking, are all sinners", and He never
remotely suggests that this same reproach can be brought against Him. He says again, "I am
begotton of the One God, before Abraham was, I am", and remember what the words "I am" were in
Hebrew. They were the name of God, which must not be spoken by any human being, the name
which it was death to utter.