Let there be light (1:3)
In 1907, when Rabbi Sholom DovBer of Lubavitch was staying at the health spa in Wirtzburg, Germany, a group of chassidim came to spend a Shabbos with the Rebbe. Among them was Reb Yosef Yuzik Horowitz, his son-in-law Reb Feivel Zalmanov, and Reb Elimelech Stoptzer.
The Rebbe prayed for many hours that Shabbos morning, as was his manner. Meanwhile, the chassidim made kiddush and consumed a respectable quantity of 'l'chayim's'. Later, when the Rebbe had finished and they sat with him to the Shabbos meal, Reb Yosef Yuzik asked:
"Rebbe, what is a chassid?"
Replied the Rebbe: "A chassid is a lamplighter. The lamplighter walks the streets carrying a flame at the end of a stick. He knows that the flame is not his. And he goes from lamp to lamp to set them alight."
Asked Reb Yosef Yuzik: "What if the lamp is in a desert?"
"Then one must go and light it," said the Rebbe. "And when one lights a lamp in a desert, the desolation of the desert becomes visible. The barren wilderness will then be ashamed before the burning lamp."
Continued the chassid: "What if the lamp is at sea?"
"Then one must undress, dive into the sea, and go light the lamp."
"And this is a chassid?" Reb Yosef Yuzik asked.
For a long while the Rebbe thought. Then he said: "Yes, this is a chassid."
"But Rebbe, I do not see the lamps!"
Answered the Rebbe: "Because you are not a lamplighter."
"How does one become a lamplighter?"
"First, you must reject the evil within yourself. Start with yourself, cleanse yourself, refine yourself, and you will see the lamp within your fellow. When a person is himself coarse, G‑d forbid, he sees coarseness; when a person is himself refined, he sees the refinement in others."
Reb Yosef Yuzik then asked: "Is one to grab the other by the throat?"
Replied the Rebbe: "By the throat, no; by the lapels, yes."

I'm not really understanding the last two paragraphs.
Could someone clear it up for me?
When attempting to save someone, we must not harm them. Grabbing someone by the throat, even metaphorically, can be harmful. So the Rebbe said that the person should be grabbed by their clothing instead.