The Talmud (Yuma 9b) states that the Second Temple was destroyed due to senseless hatred. Meaning to say, that they hated for no reason whatsoever; not for holy reasons and even contrary to basic rationale and reason.
The way to correct this is through the polar opposite—senseless love.
One should love their fellow Jew, even when there is no reason to love him. Meaning to say, that even when this love runs counter to basic rationale or what he thinks to be holy, he should nevertheless love his fellow.
(Igros Kodesh, Vol. 4 Pg. 404)
