Rav Sadya Gaon: One who joins with the living, he has hope and Bitachon. Ri Kara - after death, hope is lost, like Yisrael said "Yavshu Atzmoseinu v'Avdah Sikvasenu Nigzarnu Lanu" (Yechezkel 37:11).

Rashi: While he is alive, even if he is a Rasha and connected to Resha'im - "El Kol ha'Chayim" is even to Resha'im - there is Bitachon ¹ . Perhaps he will repent before he dies.

Ibn Ezra #1: People think that anyone connected to life has Bitachon.

Ibn Ezra #2: Which of the dead ² can connect to the living?! One cannot join to all who separate from him.

Ri Kara: Who will live forever, and not see death, and he will be connected to the living, and not to the dead?

Rid: This refutes the folly in people's hearts (that since everyone will die, a Tzadik's virtue did not help him). One who is connected to all (eternal) life, he has Bitachon for this world!

R. Avigdor: This refers to Tzadikim, who are called alive even when they are dead (Brachos 18a).

Seforno: What is connected to all aspects of living beings - sense, motion, nourishment and growth, even if some is lost.

Ibn Ezra: It is written Yivchar, for the dead cannot choose.

R. Avigdor: It says "u'Vacharta ba'Chayim Lema'an Tichyeh" (Devarim 30:19). Refer to 9:4:3:1. This is the source of a Mitzvas Aseh to choose the living, and not those who died, for there is no Bitachon in the dead.

Ibn Ezra: There is Bitachon only with the living, but not with the dead. R. Avigdor - "Tov Lachasos ba'Shem mi'Beto'ach ba'Adam" (Tehilim 118:9).

Seforno: Refer to 9:4:1:8.

Shabbos 30b, cited partially in Rashi: David died on Shabbos. Shlomo asked Chachamim - my father is dead, in the sun (the body is prone to decay), and his dogs are hungry. What should I do? They said, cut up a Nevelah for the dogs to eat. Put a loaf or child on top of your father. You may move his body together with it. (Rashi 30b - he could feed the dogs normally, but David's body (Muktzeh) he could move only via a loaf or child. Alternatively, they answered about the dogs before about David.)

Rav Sadya Gaon: It is better to join to a live dog than to a dead lion [for one who joins with the living, he has hope and Bitachon].

Rashi: Both of these refer to Resha'im. Nevuzaradan was an Eved ¹ Rasha, and he converted; death did not precede [his Teshuvah]. His master Nebuchadnetzar is called a lion - "Alah Arye mi'Subecho" (Yirmeyah 4:7), and he died in his evil. He is in Gehinom, and his servant is in Gan Eden.

Rashbam: After death, there is no ability and strength.

R. Avigdor: Via Ru'ach ha'Kodesh, this is a disgrace of a future false Mashi'ach. A live dog can help man; the dead cannot help at all.

Refer to 4:2:3:1-2.