Rabbi Gadol writes:
a) R Yisrael Salanter [1810-1883] saw as his lifelong mission to correct the often distorted emphasis, whereby piety and rituals were often emphasized unthinkingly and far more than ethical behavior, logic and bein adam lachaveiro. (Other religions did this in the Middle Ages as well, and especially the Muslims today.)
[See this week's haftarah, Yeshayah 1:11-17, that when people neglect ethical behavior toward the weak and bein adam lachaveiro, their observance of Shabbos and davening is not only worthless, but even called "an abomination" and hated by Hashem. And as reiterated by many neviim, esp the haftarah of Yom Kippur, Yeshayah 58:5-7.]
b) (Gittin 56a, and studied on Tisha B'Av) The tana R Zecharyah ben Evkolas, is blamed in the Gemara for causing the entire churban by being too machmir (stringent) on a ritual law of sacrifices when the lives of the entire Jewish people would be endangered. [See Mesillas Yesharim ch 20, who emphasizes this.]
c) [ The Chazon Ish (1878-1953) said that it is not logical, although perhaps quite understandable, and especially nowadays, that many people tend to think (without studying history or having been there) that the worst sins in Europe before the war were the mass forsaking of Shabbos and kashrus and all the ritual mitzvos.
Actually there were very powerful mitigating reasons for this [and most had long been assimilated for a century in Western Europe and knew nothing, as many gedolim pointed out, or had Jewish life and education in Eastern Europe totally disrupted after WW I. Plus the enforced atheism and mass suffering of millions of Jews in Russia in 1917, plus mass anti-Semitism for centuries all over Europe, which caused even many sincere Jews to naturally be drawn to new ideas and movements to end the unbearable Jewish suffering and poverty, etc. See Bava Basra 16b, 14th line "a person is not to be blamed when suffering excessively".]
Rather, the worst sins worth emphasizing, he said, to people who remember well, were the often poor bein adam lachaveiro, contentiousness, divisiveness, rivalries between groups, machlokes and Chilul Hashem among the ultra-Orthodox Jews and others, who might have known better. See also Netziv, preface to Sefer Breishis, about this before the second churban [Yoma 9b - sinas chinam]. And many other such sources.
(See also letter of the Chofetz Chaim about the widespread machlokes, divisiveness and pashkvilim [posters, sheets] among the Chareidim before the war, in Europe and especially in Israel and the old yishuv, which, like the Chazon Ish, he also regarded with the utmost gravity. See also memoirs of the son of the Chofetz Chaim about his visit to Israel. Thankfully, it has been noted that in America and Western countries, much of this is relatively quite absent from the Jewish communities.)
("Minchas Nosson" on Kiddushin ch 27, from a Ger chassid in Beer Sheva, R Nosson Einfeld. See similarly in preface to Chassidisher sefer Kol Mevaser. See also Chazon Ish Emunah & Bitachon 1:14 end, 2:3 end, 3:9 quoting RY Salanter, 4:5 that a person with poor and inconsiderate bein adam lachaveiro really has little bein adam lamakom as well.) ]
Stories of R Yisrael Salanter
1) On his way to get water for netilas yadayim, a disciple of R Yisrael passed through some rooms in which people were sleeping. "Netilas yadayim is a mitzvah derabbanan", commented R Yisrael, "but robbing others of their sleep or disturbing people is forbidden by the Torah" (ve'ahavta le'reiacha kamocha) (Sparks of M, page 21)
2) A man rushed into shul to answer kedushah in the winter. In his haste, he stepped on the shoes of one of the people and dirtied them. After kedushah, R Yisrael called the man over, and told him to apologize to the person he stepped on. "True, kedushah is a precious mitzvah", he said. "But what good is it if one ruins it by harming someone else?" (47)
3) Once, R Yisrael's host in a certain village said "Rebbe, this time you can perform netilas yadayim with as much water as you like. I now have a Jewish maid who helps us with all the hard work of drawing water and preparing food."
R Yisrael answered, "Thank you, but I have no intention of doing a hidur mitzvah by bending the shoulders of a poor orphan girl." (25)
4) Even in his last hours, R Yisrael did not stop thinking about bein adam lachaveiro and how to help others, as was his lifelong emphasis and mission.
On the last day of his life, in Koenigsberg, Germany, a simple Jew was sent to help attend him. In his last hours, R Yisrael began a conversation with the man about how some people may fear being alone with a corpse. He assured him that there is nothing at all to be afraid of, and that a dead person can't harm anyone at all. Soon after he passed away, with no one present except the attendant. (57)
"The way to fulfill the mitzvah of loving Hashem [and Kiddush Hashem] is by beautiful and friendly behavior towards others." [Yoma 86a]
"You're never more like God than when you help and encourage people." (See also Sotah 14a, middle, the ways of Hashem)
May the entire Am Yisrael and world see an end to all the suffering of humanity, and know only happiness from now on.