Now the sons of Reuben the firstborn of Israel, (for he was the firstborn; but, since he defiled his father's bed, his birthright was given unto the sons of Joseph the son of Israel: and the genealogy is not to be recorded according to the birthright.
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George Leo Haydock
First-born, Genesis xlix. 4. (Worthington)
He gives this reason for not beginning with him. (Calmet)
And he. Protestants, "and the genealogy is not to be reckoned after the birth-right. "(Haydock)