"The youth who stands at the beginning of life says with the same right as the old man who stands at the end of life and gazes out over the past: One suffers only once. With the same right – that is, by virtue of the eternal, but not with the same truth, even if the statement is equally true. The youth says what is true, but the old man has verified it, has made true that which is indeed eternally true. This is the only difference, something that has been overlooked in these times, in which people with all this demonstrating and demonstrating have completely forgotten that the highest a person is capable of is to make [gjore] an eternal truth true, to make it true that it is true – by doing [gjore] it, by being oneself the demonstration, by a life that perhaps will also be able to convince others. Did Christ ever get involved in demonstrating one or another truth, or in demonstrating the truth? No, but he made the truth true, or he made it true that he is the truth."
January 1, 1970
https://en.wikiquote.org/wiki/Eternity