Genèse 6:3

And the Lord said by His Word, All the generations of the wicked which are to arise shall not be purged after the order of the judgments of the generation of the deluge, which shall be destroyed and exterminated from the midst of the world. Have I not imparted My Holy Spirit to them, (or, placed My Holy Spirit in them,) that they may work good works? And, behold, their works are wicked. Behold, I will give them a prolongment of a hundred and twenty years, that they may work repentance, and not perish.

‘BESHAGAM’ (FOR THAT ALSO) HE IS FLESH. It is as if beshagam were written beshegam with a segol under the shin. And Rashi explained: “This quality is also in him, that he is only flesh, and yet he is not humble before Me. What would he do if he were made of fire or some hard substance.” This explanation has neither rhyme nor reason.
Rabbi Abraham ibn Ezra explained that G-d said, “My spirit will not abide in man forever because of this violence and also because man is flesh, and when he reaches a certain age he disintegrates.” Ibn Ezra thus understands the verse as if it said, gam beshehu basar (also because he is flesh). But what need is there for stating this contention when it is known that they were but flesh. and death had been decreed on them, as it says, For dust thou art, and unto dust shalt thou return?
The correct interpretation appears to me to be that G-d said: “My spirit shall not abide in man forever because man also is flesh as all flesh that creepeth upon the earth in the forms of fowl and cattle and beast, and it is not fitting that the spirit of G-d be within him.” The purport is to state that G-d made man upright to be like the ministering angels by virtue of the soul He gave him. But he was drawn after the flesh and corporeal desires; he is like the beasts that perish, and therefore the spirit of G-d will no longer be sheathed in him for he is corporeal and not godly. However, He will prolong for them [this withdrawal of spirit] if they repent. The sense of this verse is thus similar to [the verse in Psalm 78]: So He remembered that they were but flesh, a wind that passeth away, and cometh not again.

לא ידון, G’d says that He cannot continue to weigh if to destroy mankind or not constantly, בשגם, although He is making allowances בשר, for the fact that they are largely composed of flesh; nonetheless they keep deteriorating so that He is forced to put an end to them.

לא ידון רוחי באדם לעולם בשגם הוא בשר, it is intolerable that there will continue the argument, strife before Me allowing (the angels?) to claim that although seeing that man has been endowed with divine qualities he must be punished, whereas his close ties to physical earth must be considered as excuses for his conduct, entitling him to continued mercy, and indulgence by Me.

והיו ימיו, he will be given a certain length of time within which to repent his sins;

מאה ועשרים שנה, during which time Noach would have time to construct the ark, and by doing so rebuking and warning people of what is in store for them. (compare Sanhedrin 108)

ויאמר ה' לא ידון רוחי באדם לעולם, G’d either said this to Himself, or to Noach. My father of blessed memory (Joseph Kimchi) explained the line לא ידון in the same sense as the word מדון in Proverbs 15,18 as referring to a struggle, strife. The soul G’d had blown into Adam’s nostrils was meant as an antidote to the pull of the raw material man was made of. The body, basically is in tow of the animalistic urges of the animals, something natural, seeing that man’s own body is made of the same raw material as are the animals. G’d now decided to grant man an extension of 120 years to do תשובה, repentance, failing which He would wipe out mankind from the earth. Other commentators, including Ibn Ezra, explain the word ידון as related to נדנה in Chronicles I 21,27 וישב חרבו אל נדנה, “he returned his sword to its sheath.” Actually, if correct, the word ידון should have been spelled with a dagesh in the letterד, replacing the missing letter נ, however, in this instance, instead of such a dagesh, the Torah simply omitted the letter נ at the beginning, as it did in Genesis 25,29 ויזד יעקב נזיד where the letter נ in front of the letter ז has also been omitted. At any rate, the meaning of the expression is that G’d would not let His spirit rest until both man’s body and spirit would be wiped out.
Rabbi Yishmael son of Yossi, (Bereshit Rabbah 26,6) understood this verse as G’d saying that when the time would come to share out reward to the righteous, these people would not participate in it. He was speaking of ידון in the sense of “passing judgment.” Rabbi Shimon ben Lakish as well as his colleague Rabbi Yannai, said that there is no such thing as the popular concept of a hell, gehinnom, lasting a long time, but that at the time when G’d passes out judgment the wicked will be burned by the fiery heat of a flame. They based themselves on Maleachi 3,19 הנה יום בא בוער כתנור, “here a day will come when the fire will burn as in a furnace.” The other sages said that there most certainly is such a thing as gehinnom, as we have a verse in Isaiah 31,9 נאום ה' אשר אור לו בציון ותנור לו בירושלים, “says the Lord Who has a fire in Zion and an oven in Jerusalem.” Rabbi Yehudah bar Ila-i claims there is neither a specific day, nor a specific place such as gehinnom, but fire will come forth from the very bodies of the wicked and will consume them with its heat. He based himself on Isaiah 33,11 תהרו חשש תלדו קש רוחכם אש תאכלתם, “you shall conceive hay, give birth to straw; My breath will devour you like fire.”
We have also written what the sages of the Midrash wrote concerning the matter of gehinnom in connection with Genesis 1,31 וירא אלוקים את כל אשר עשה והנה טוב מאד, “G’d saw all that He had made and here it was very good;” the point made there was that the word טוב refers to Gan Eden, whereas the expression טוב מאד, refers to gehinnom. [refer to page 72 in my translation. Ed.] Rabbi Yehudah in the name of Rabbi Ila-i (also in Bereshit Rabbah 26,6) interprets the words לא ידון רוחי עוד, that “these wicked spirits of man will never be allowed to come to rest before Me.” Various sages concur that the generation destroyed during the deluge will neither be judged for an afterlife during the time that the world awaits its own rejuvenation, nor will it be judged (if any are fit) to be resurrected in the world following the interval between our present world being turned into chaos and the subsequent resurrection of the deserving from the former world. (Sanhedrin 107)

לא ידון רוחי באדם לעולם, “My spirit will not rule within man forever;” this is a metaphor describing G–d as withholding man’s souls from participating in an afterlife after they had returned for Divine judgment. An alternate explanation: “I will no longer equip man with a heavenly soul.” (B’reyshit Rabbah 26,6.)

בשגם הוא בשר, this word is an acrostic, the numerical value of its letters totalling 345, as does the numerical value of the letters in the word משה, (Moses) Moses lived for 120 years, meaning that he demonstrated that during 120 years on earth the human being can attain earthly perfection. This presupposes that such a human being had lived by the laws of the Torah. If man had not become corrupted, he could have attained such perfection by his own efforts without having to observe all the laws of the Torah, but it would have taken longer. This is why originally he was allowed to live to almost become one thousand years old. Once man only has a לב בשר, “a heart of flesh,” this process had to be drastically changed. [I have borrowed from the commentary of Rabbi Elie Munk in his “The call of the Torah.” Ed.]