He is widely regarded as one of the most important Jewish figures of his time, and his escape from the Roman destruction of Jerusalem (which allowed him to continue teaching) may have been instrumental in Rabbinic Judaism's survival post-Temple.
[6][7] Although living among them, he found the attitude of Galileans to be objectionable, allegedly exclaiming that they hated the Torah and would therefore "fall into the hands of robbers.
During the siege of Jerusalem in 70 CE in the First Jewish–Roman War, he argued in favour of peace: according to the Talmud (Gittin 56a), when he found the anger of the besieged populace to be intolerable, he arranged a secret escape from the city inside a coffin, helped by his nephew and Zealot leader Ben Batiach, so that he could negotiate with Vespasian (who, at this time, was still just a military commander).
In return, Vespasian granted Yochanan three wishes: the salvation of Yavne and its sages and the descendants of Rabban Gamliel, who was of the Davidic line, and a physician to treat Rabbi Zadok, who had fasted for 40 years to stave off the destruction of Jerusalem.
[10] His school functioned as a re-establishment of the Sanhedrin so that Judaism could decide how to deal with the loss of the sacrificial altars of the temple in Jerusalem and other pertinent questions.
[14] His students were present at his deathbed and were requested by him, in his penultimate words according to the Talmudic record, to reduce their risk of ritual contamination conveyed by a corpse: Put the vessels out of the house, that they may not become unclean...[15]More enigmatic were the Talmud's record of his last words, which seem to relate to Jewish messianism:[6] ...prepare a throne for Hezekiah, the King of Judah, who is coming[15]According to the Talmud, Yochanan ben Zakkai lived 120 years.
The following story is told in the Jewish classic, Avoth deRabbi Nathan, version B, chapter 4:5, about the war with Rome.
(i.e., the reference is to the Roman general Cestius who was defeated by the Judeans in 66 CE, marking the beginning of the war with Rome).
When our Master, Yochanan ben Zakkai, heard these words, he called out to the men of Jerusalem and said to them: 'My sons, why would you destroy this city, or seek to burn down the holy house!?
I will go and teach therein my disciples, and I'll establish therein prayer, and I'll perform therein all of the duties prescribed in the divine Law.'
They said that no more than two or three days had passed when a certain messenger came from his city, informing him that Caesar had just died, and that they have nominated him to head the Roman Empire.
When Rabban Yochanan ben Zakkai heard that he (i.e., Caesar's son, Titus, who was left to govern the Roman army) destroyed Jerusalem and burnt down the holy house with fire, he rent his clothes, and his disciples rent their clothes, and they were crying and shouting and pounding their chests as mourners, etc.Jewish tradition records Yohanan ben Zakkai as being extremely dedicated to religious study, claiming that no one ever found him engaged in anything but study.
[18] On one occasion he advises that mankind should seek to understand the infinity of God, by imagining the heavens being extended to unthinkable distances.
[25] He was challenged to resolve several biblical curiosities by a Roman commander, who was familiar with the Torah, but whose name has been lost in confusion.