ר׳ אהבה בר׳ זעירא אמר אף התשובה הה״ד בטרם הרים וגו׳ (שם צ ב) מאותה השעה תשב אנוש עד דכא ותאמר שובו (שם שם ג,
R. Ahbah bar Zeira said, “Also repentance. This is as it is written, ‘Before the mountains [were brought forth or you had formed the earth and the world, from everlasting to everlasting, you are God’] (Psa. 90:2). From that hour: ‘You return man to dust and say, Return, [O children of man’] (Psa. 90:3).This section appears to be a later insertion. I don't know how rabbinic scholars would determine this, but here's my reasoning. First, we started out with a list of six things. The list is complete: 1) the Torah, 2) the throne of glory, 3) the patriarchs, 4) Israel, 5) the Temple, and 6) the name of the Messiah. So, "repentance" is added here as the seventh item in the list. Second, the style shifted when an interloper entered the discussion - R. Ahbah bar Zeira. This interjection breaks the logical connection between what came before and what will come after. The use of Scriptural support is not as neat and succinct as the earlier items. It is as if a later reader was following the discussion and couldn't help but interject with yet another text that somehow seemed to him to be relevant. R. Ahbah reminds me a bit of Elihu in Job 33-37. Fortunately for us, Ahbah is not nearly the windbag and blowhard that Elihu is. He throws in his couple of lines and goes away, for the moment. I wonder if it just really bothered them to have a list of only six things when we all know that lists of seven are so much better.