Why does it mention multiplying?
Radak: Even though you will increase in the land, the Goyim will not envy you and come to fight with you, that you would need to bring Aron ha'Elokim with you. The custom was to take the Aron to war. Then (in the future) you will not need to, for you will not have war again.
Malbim: After you will be few number at the time - "Echad me'Ir u'Shenayim mi'Mishpachah" (verse 14) - you will increase.
Why will they no longer say "Aron Bris Hashem"?
Rashi: All your gathering will be Kadosh. I will dwell in it as if it is the Aron.
Malbim: Now, speech and thought are not connected. People mention Kedushah of Aron ha'Bris and words of the Torah in it, but their heart is distant and they do not think about them. And even when they think about the Aron, they do not act according to the Bris. In the future, it will not be so. They will be Tzadikim - "v'Hayah ha'Nish'ar b'Tziyon
What is the meaning of "Lo Yifkedu"?
Rashi: They will not be remembered.
What will not be done again?
Rashi: They will not repeat what happened at Shilo, that they brought the Aron to the war with Pelishtim in the days of Eli.
Radak: They will not have war again.
Malbim: They will not think about the Aron without acting according to the Bris (like people do today). Deed, action and thought will be united!
