Jesus didn’t write it. Others wrote down what they heard. But this happens throughout time and there is a Greater Book one can read that goes on endlessly. One that Jesus read with his body and life. It was not the time to reveal that. He revealed that later.
"Ay, many kotis of years they may pass without ever having mentioned my name, the law, or my congregation. That is the fruit of sinful deeds.
But when mild and gentle beings are born in this world of men, they immediately see me revealing the law, owing to their good works.
I never speak to them of the infinitude of my action. Therefore, I am, properly, existing since long, and yet declare: The Ginas are rare (or precious).
Such is the glorious power of my wisdom that knows no limit, and the duration of my life is as long as an endless period; I have acquired it after previously following a due course.
Feel no doubt concerning it, O sages, and leave off all uncertainty: the word I here pronounce is really true; my word is never false.
For even as that physician skilled in devices, for the sake of his sons whose notions were perverted, said that he had died although he was still alive, and even as no sensible man, would charge that physician with falsehood;
So am I the father of the world, the Self born, the Healer, the Protector of all creatures. Knowing them to be perverted, infatuated, and ignorant I teach final rest, myself not being at rest."