My strength, &c. He calls him his strength, as being born whilst his father was in his full strength and vigour: he calls him the beginning of his sorrow, because cares and sorrows usually come on with the birth of children. — Excelling in gifts, &c., because the first-born had a title to a double portion, and to have the command over his brethren, which Ruben forfeited by his sin; being poured out as water; that is, spilt and lost. (Challoner) — In command. He ought to have succeeded to his father in authority. But Joseph entered in upon his rejection, 1 Paralipomenon v. 1. The priesthood was given to Levi’s descendants; and the regal power, partly to those of Joseph, who reigned over the ten tribes, for a long time; and partly to the posterity of Juda, who exercised dominion over all the people of Israel. (Chaldee) (Worthington)

Matthew Henry Commentary on the Whole Bible (Complete) (Matthew Henry)

II. The prophecy concerning Reuben. He begins with him (v. 3, 4), for he was the firstborn; but by committing uncleanness with his father's wife, to the great reproach of the family to which he ought to have been an ornament, he forfeited the prerogatives of the birthright; and his dying father here solemnly degrades him, though he does not disown nor disinherit him: he shall have all the privileges of a son, but not of a firstborn. We have reason to think Reuben had repented of his sin, and it was pardoned; yet it was a necessary piece of justice, in detestation of the villany, and for warning to others, to put this mark of disgrace upon him. Now according to the method of degrading, 1. Jacob here puts upon him the ornaments of the birthright (v. 3), that he and all his brethren might see what he had forfeited, and, in that, might see the evil of the sin: as the firstborn, he was his father's joy, almost his pride, being the beginning of his strength. How welcome he was to his parents his name bespeaks, Reuben, See a son. To him belonged the excellency of dignity above his brethren, and some power over them. Christ Jesus is the firstborn among many brethren, and to him, of right, belong the most excellent power and dignity: his church also, through him, is a church of firstborn. 2. He then strips him of these ornaments (v. 4), lifts him up, that he may cast him down, by that one word, "Thou shalt not excel; a being thou shalt have as a tribe, but not an excellency." No judge, prophet, nor prince, is found of that tribe, nor any person of renown except Dathan and Abiram, who were noted for their impious rebellion against Moses. That tribe, as not aiming to excel, meanly chose a settlement on the other side Jordan. Reuben himself seems to have lost all that influence upon his brethren to which his birthright entitled him; for when he spoke unto them they would not hear, ch. 42 22. Those that have not understanding and spirit to support the honours and privileges of their birth will soon lose them, and retain only the name of them. The character fastened upon Reuben, for which he is laid under this mark of infamy, is that he was unstable as water. (1.) His virtue was unstable; he had not the government of himself and his own appetites: sometimes he would be very regular and orderly, but at other times he deviated into the wildest courses. Note, Instability is the ruin of men's excellency. Men do not thrive because they do not fix. (2.) His honour consequently was unstable; it departed from him, vanished into smoke, and became as water spilt upon the ground. Note, Those that throw away their virtue must not expect to save their reputation. Jacob charges him particularly with the sin for which he was thus disgraced: Thou wentest up to thy father's bed. It was forty years ago that he had been guilty of this sin, yet now it is remembered against him. Note, As time will not of itself wear off the guilt of any sin from the conscience, so there are some sins whose stains it will not wipe off from the good name, especially seventh-commandment sins. Reuben's sin left an indelible mark of infamy upon his family, a dishonour that was a wound not to be healed without a scar, Prov 6 32, 33. Let us never do evil, and then we need not fear being told of it.

Matthew Henry Commentary on the Whole Bible (Concise) (Matthew Henry)

Verses 3-7 Reuben was the first-born; but by gross sin, he forfeited the birthright. The character of Reuben is, that he was unstable as water. Men do not thrive, because they do not fix. Reuben's sin left a lasting infamy upon his family. Let us never do evil, then we need not fear being told of it. Simeon and Levi were passionate and revengeful. The murder of the Shechemites is a proof of this. Jacob protested against that barbarous act. Our soul is our honour; by its powers we are distinguished from, and raised above, the beasts that perish. We ought, from our hearts, to abhor all bloody and mischievous men. Cursed be their anger. Jacob does not curse their persons, but their lusts. I will divide them. The sentence as it respects Levi was turned into a blessing. This tribe performed an acceptable service in their zeal against the worshippers of the golden calf, ( Exodus 32 ) . Being set apart to God as priests, they were in that character scattered through the nation of Israel.