The Sages assert that the First Temple was destroyed due to the grave transgressions of idolatry, bloodshed, and forbidden sexual relations. By contrast, the destruction of the Second Temple was due to a single sin: Gratuitous hatred.

Jerusalem was destroyed on account of Kamtza and bar Kamtza. As there was a certain man whose friend was Kamtza and whose enemy was bar Kamtza. That man made a feast and said to his servant: Go bring me Kamtza. He went and brought him bar Kamtza instead.

The host came and found bar Kamtza sitting at his feast. He said to bar Kamtza: This man [referring to himself] is the enemy of that man [you]. What do you seek here? Bar Kamtza said to him: Since I came, let me stay, and I will pay you for the cost of what I eat and drink.

The host said to him: No. Bar Kamtza said to him: I will give you half the cost of the feast. The host said to him: No. Bar Kamtza said to him: I will give you the cost of the entire feast. He said to him: No. The host seized bar Kamtza by the hand, stood him up, and took him outside.

Bar Kamtza said to himself: Since the Sages were sitting there and did not protest the host’s actions, they apparently were comfortable with his conduct. I will go and inform against them at the palace. Bar Kamtza went and said to the emperor: The Jews have rebelled against you. The emperor said to him: Who says so? Bar Kamtza said to him: Send them an offering to be brought on your behalf, and see whether they sacrifice it.

The emperor sent a choice calf with him. As bar Kamtza was en route to the Temple, he inflicted a blemish on the calf’s upper lip. Some say it was on its eyelids, a place that for us is considered a blemish; but according to them it is not a blemish.

The Sages thought to sacrifice the calf despite the blemish due to the obligation to maintain peaceful relations with the government. Rabbi Zekharya ben Avkolas said to them: People will say that blemished animals may be offered on the altar. The Sages thought to kill bar Kamtza so that he would not go and tell the authorities. Rabbi Zekharya said to them: People will say that one who inflicts a blemish on consecrated animals is liable to be executed.

Rabbi Yohanan said: The humility of Rabbi Zekharya ben Avkolas destroyed our Temple, burned our Sanctuary, and exiled us from our land. (Gittin 55b–56a)