Adam Clarke on Genesis 49:4

Pouring out like the waters - This is an obscure sentence because unfinished. It evidently relates to the defilement of his father's couch; and the word פחז pachaz, here translated pouring out, and in our Version unstable, has a bad meaning in other places of the Scripture, being applied to dissolute, debauched, and licentious conduct. See Jdg 9:4; Zep 3:4; Jer 23:14, Jer 23:32; Jer 29:23.

Thou shalt not excel - This tribe never rose to any eminence in Israel; was not so numerous by one third as either Judah, Joseph, or Dan, when Moses took the sum of them in the wilderness, Num 1:21; and was among the first that were carried into captivity, 1Chr 5:26.

Then thou didst defile - Another unfinished sentence, similar to the former, and upon the same subject, passing over a transaction covertly, which delicacy forbade Jacob to enlarge on. For the crime of Reuben, see Clarke on Gen 35:22 (note).

5. Simeon and Levi, brethren: They have accomplished their fraudulent purposes.

6. Into their secret council my soul did not come; In their confederacy my honor was not united: For in their anger they slew a man, (איש ish, a noble), And in their pleasure they murdered a prince.

7. Cursed was their anger, for it was fierce! And their excessive wrath, for it was inflexible! I will divide them out in Jacob, And I will disperse them in Israel.