copied:
Chazal inform us that the primary cause for the destruction of the second Beis HaMikdash was Sinas Chinam. In this context, the Gemara in Gitin famously ascribes partial blame to the story of Kamtza and Bar Kamtza. I think most of us are familiar with the incident where an unnamed individual threw a celebration and mistakenly invited his rival Bar Kamtza in place of his friend Kamtza. When the error was discovered, he insisted on ejecting Bar Kamtza despite repeated entreaties. In revenge, Bar Kamtza incited the Roman Emperor on a path that ultimately led to the siege of Yerushalaim and the destruction of the Beis HaMikdash.
The question arises, why does Kamtza share the responsibility equally with Bar Kamtza; he had absolutely no stated role in the events? And why is the host whose rigid hate and stubbornness to humiliate Bar Kamtza not named?
Chazal tell us that one do did not merit the rebuilding of the Beis HaMikdash in his days is as if it was destroyed in his days. The implication being that if we had eradicated the Sinas Chinam that led to the Churban, we would immediately merit its rebuilding, and we are held accountable for not doing our part.
May we all deserve to see the Third Beis HaMikdash soon.