In reading about Reuven's sin, we come across an interesting phenomenon. In one verse, the Torah describes Reuven's sin (read more details on the approaches to Reuven's sin here). However, before the verse is completed, the Torah begins a new paragraph with the words "And Yaakov's sons were twelve" and continues to name each of the sons according to their mothers.
What is the Torah trying to tell us by merging two paragraphs into one verse?
With regard to the children of Avraham, Yishmael was rejected because he was the son of Hagar, the maidservant.
With regard to Yitzhak's children, Esav was rejected, though he was the daughter of Rivka, because of his choices and actions.
Is the same process to be expected with the children of Yaakov? Will sons be rejected based on their lineage and actions?
To answer this question the Torah merges the two separate, seemingly unrelated paragraphs into one verse! Reuven did sin, but he is not rejected. He remains one of Yaakov's 12 sons and even the firstborn (see Rashi on verse 23). Additionally, Bilha and Zilpa's children are introduced as the children of the maidservants and nonetheless, they too are counted as Yaakov's twelve sons.
Thus, the system of rejections, an existent and necessary system with regard to the first two generations, is itself rejected in Yaakov's family, the third and defining generation of the nation.