Reuben, thou art my firstborn
Jacob addressed himself to Reuben first, in the presence of his brethren, owned him as his firstborn, as he was, ( Genesis 29:31 Genesis 29:32 ) did not cashier him from his family, nor disinherit him, though he had greatly disobliged him, for which the birthright, and the privileges of it, were taken from him, ( 1 Chronicles 5:1 1 Chronicles 5:2 ) my might, and the beginning of my strength;
begotten by him when in his full strength F26, as well as the first of his family, in which his strength and glory lay; so the Septuagint, "the beginning of my children"; and because he was so, of right the double portion belonged to him, had he not forfeited it, ( Deuteronomy 21:17 ) ( Psalms 105:36 ) . Some versions render the words, "the beginning of my grief", or "sorrow" F1, the word "Oni" sometimes so signifying, as Rachel called her youngest son "Benoni", the son of my sorrow; but this is not true of Reuben, he was not the beginning of Jacob's sorrow, for the ravishing of Dinah, and the slaughter and spoil of the Shechemites, by his sons, which gave him great sorrow and grief, were before the affair of Reuben's lying with Bilhah: the excellency of dignity, and the excellency of power;
that is, to him of right belonged excellent dignity, power, and authority in the family, a preeminence over his brethren, a double portion of goods, succession in government, and, as is commonly understood, the exercise of the priesthood; and so the Targums interpret it, that he should, had he not sinned, took three parts or portions above his brethren, the birthright, priesthood, and kingdom. Jacob observes this to him, that he might know what he had lost by sinning, and from what excellency and dignity, grandeur and power, he was fallen.
The Brenton translation of the Septuagint is in the public domain.