וַיְהִ֗י בִּשְׁכֹּ֤ן יִשְׂרָאֵל֙ בָּאָ֣רֶץ הַהִ֔וא וַיֵּ֣לֶךְ רְאוּבֵ֗֔ן וַיִּשְׁכַּ֕ב֙ אֶת־בִּלְהָ֖ה֙ פִּילֶ֣גֶשׁ אָבִ֑֔יו וַיִּשְׁמַ֖ע יִשְׂרָאֵ֑͏ֽל׃ {פ}
וַיִּֽהְי֥וּ בְנֵֽי־יַעֲקֹ֖ב שְׁנֵ֥ים עָשָֽׂר׃
While Israel stayed in that land, Reuben went and lay with Bilhah, his father’s concubine; and Israel found out.
Now the sons of Jacob were twelve in number.
בְּנֵ֣י לֵאָ֔ה בְּכ֥וֹר יַעֲקֹ֖ב רְאוּבֵ֑ן וְשִׁמְעוֹן֙ וְלֵוִ֣י וִֽיהוּדָ֔ה וְיִשָּׂשכָ֖ר וּזְבֻלֽוּן׃
The sons of Leah: Reuben—Jacob’s first-born—Simeon, Levi, Judah, Issachar, and Zebulun. Genesis 35:22-23 (Revised JPS, 2023)
In one verse, Reuben is shown to commit the most grevious sin. In the next, Reuben is not only listed among the twelve, his status as "first born" is clearly maintained.
In Genesis 49, Jacob says of Reuben: "uncontrollable as water, you shall not have preeminence." However, in Deuteronomy 33, Moses says of Reuben: "May Reuben live and not die, nor may his people be few."
I can't help but view Reuben's story as one of moral failing, but not of total rejection. While Reuben loses authority and the blessings of the firstborn (which will be passed to Judah and Joseph), he is not cut off from his people.
Perhaps this is also a story about how the moral failings of leaders should be handled.