Reuben, thou art my firstborn, my {b} might, and the beginning of my strength, {c} the excellency of dignity, and the excellency of power:

(b) Begotten in my youth.

(c) If you have not left your birthright by your offence.

Wesley's Notes

49:3 Reuben thou art my first - born - Jacob here puts upon him the ornaments of the birth - right, that he and all his brethren might see what he had forfeited and in that might see the evil of his sin. As the first - born he was his father's joy, being the beginning of his strength. To him belonged the excellency of dignity above his brethren, and some power over them.

Jamieson-Fausset-Brown Bible Commentary

Ge 49:3, 4. Reuben forfeited by his crime the rights and honors of primogeniture. His posterity never made any figure; no judge, prophet, nor ruler, sprang from this tribe.

Matthew Henry's Concise Commentary

49:3-7 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, Ex 32. Being set apart to God as priests, they were in that character scattered through the nation of Israel.