He recalls Mishna Avot's famous statement “What is hated to you, do not to do
your friend.”
Rav Schwartz emphasizes the importance of refraining from any evil toward another Jew, or being inconsiderate toward a fellow Jew.
Only then can you move on to the next step: "V'ahavta l're'echa kamocha - You shall love to you fellow like yourself."
http://www.bilvavi.net/files/Bilvavi.on.the.Three.Weeks.5778.pdf
(Scroll down to the teal banner inscribed with AHAVAS YISRAEL)
We're Defined by What We DON'T Do
Sur m'ra really is the first step.
For example, many people eat kosher food, but they also eat non-kosher food. Some keep kosher at home and abandon kashrut at restaurants.
Are they really keeping kosher?
No. They're ingesting treif food. Even those fool themselves into being makpid to eat only dairy or pareve at non-kosher restaurants still eat food that was cooked right alongside with pepperoni or bacon.
If they want to truly keep kosher, they need to "sur" from all the treif stuff.
Likewise, we all know people who eat the Leil Shabbat seuda, complete with Kiddush and Hamotzi. They light Shabbat candles and may even go to services Shabbat morning.
But they drive. They go out for ice cream. They flick light switches and watch TV. They are totally mechalel Shabbat.
Does their heartfelt Kiddush Friday night mean they are shomer Shabbat? Definitely not. They are mechalel Shabbat.
Same thing with women who cover their hair and wear miniskirts. Is that tsanuah? Yeah, her head is tsanuah, but the rest of her is not.
So sur m'ra really is more than the first step in a mitzvah; it often defines the mitzvah.
And just to be clear: I'm not saying that covering your hair while wearing un-tsnius clothing is meaningless, nor am I saying that keeping positive Shabbat commandments while running roughshod over the prohibitions is meaningless.
It's not.
(Please see If Someone is Eating a Treif Salami, Should He Make a Bracha? for more on that topic.)
But you cannot say that the person is shomer Shabbat, keeping kosher, or overall tsanuah, or whatever, until they start obeying the sur m'ra.
Anyway, sur m'ra is a good aspect to focus on at this time of the 3 Weeks.
Ahavat Yisrael? One step at a time.
First...refrain. Hold back.
Refrain from hurting people.
Refrain from inconsiderate behavior.
Refrain. Resist. Sur m'ra.