Comentario sobre Génesis 5:28

ויולד בן AND HE BEGOT A SON (בן “son”, connected with the root בנה ‘‘to build”) — from whom the world was built up (peopled) (Tanchuma 1:1:11)

ויולד בן ויקרא את שמו נח, “he fathered a son and he called his name Noach.” The number 10 is crucial to the world and its continued existence. Noach was the tenth generation of the human species. It was therefore appropriate that he became instrumental in assuring the continued existence of the world, and, more specifically, mankind. Seeing that the rest of mankind was slated to perish during the deluge and none of them proclaimed the name of G’d you do not find the word בן, “son,” or the word שם, “name“ (allusion to the name of G’d) mentioned in connection with the birth of any of the other people listed in the Torah since Sheth. In Noach’s case, the word בן is not so much a description of his being a son,” but it is related to בנה, “built,” i.e. this person rebuilt the world after the deluge and assured its continued existence. In other words: this “son” was a “builder.”
We find further that the very word שם refers to maintaining something, preventing it from decaying. When Solomon said in Proverbs 10,7 ושם רשעים ירקב, that the “name of the wicked will rot,” this may strike us as strange at first glance seeing that שם, “name,” is something abstract and if so how could something abstract be subject to decay? However, Solomon referred to the actual subject of the שם, “name,” he spoke about.
There is another question in connection with Noach. According to what Lemech, Noach’s father is reported to have exclaimed when his son was born, he should have called him מנחם, “comforter.” Perhaps the letter מ in the word מנחם was somehow “swallowed,” and Noach’s real name was נחם. We have a similar construction in Zechariah 11,7 where the prophet says לאחד קראתי נעם ולאחד קראתי חבלים, “one I named Favour, the other Unity.” According to the normal rules of grammar the word should have been מנעם. However, we find frequent instances when a word is slightly abbreviated. In this instance, the reason may have been to make the name נח also spell חן (with the letters reversed) ,as it was he who found חן in the eyes of G’d.
The reason Noach’s father Lemech said of this son זה, “this one,” may be that he was part (maybe the first) of the tenth generation of mankind, and, as we pointed out earlier, any “tenth” is holy. There is a similarity here to Exodus 15,2 זה א-לי ואנוהו, “this is my G’d and I will enshrine Him.” Lemech meant hat there were two reasons why he called “this one” Noach. This is reflected in the two cantillations on that very short word, i.e. it has both the tone-sign telisha and the tone-sign geresh. Do not be flippant about this as the entire Torah is full of all kinds of hints and allusions which have been written at the command of the Supreme Intellect. Anyone who delves into unraveling the secrets hidden in the text pays attention to every detail. This is why the sages said (Nedarim 37) that the cantillations also originated at Mount Sinai. When Nechemiah 8,8 speaks of ושום שכל ויבינו במקרא, “with careful analysis so that they could understand it,” he referred to 1) the text itself, 2) the cantillations.

From whom the world was built up. Rashi is answering the question: Why does it say בן here, and not for other descendants? It simply should have written ויולד את נח. Perforce, בן connotes בנין (building).