If I remember correctly, Rabbi Avrahom Yitzchok HaKohen Cook [ZTL & ZYA]
famously taught that:
“Since the Beth HaMikdash was destroyed by Sinat Chinam,
the Beth HaMikdash can only be rebuilt by Ahavat Chinam,”
(Or something very similar to that.)
Please forgive me for not providing an exact source for this very important quote.