신명기 21:17의 주석

פי שנים A DOUBLE PORTION — i.e. a portion equal to those of two brothers together (Sifrei Devarim 217:2-4).

כי את הבכור, the word כי means אלא, but. כי הוא ראשית אונו, for he is entitled to inherit the first of his father’s money. We find that the word און appears in this sense in Hoseah 12,9 מצאתי און לי, [clearly it cannot mean “I have found my virility there”, as it does in Genesis 49,3. Ed.] The word און also occurs in the sense of money in Job 20,10 וידיו תשיבנה אונו, “his own hands must give back his wealth.”

Equivalent to two brothers. Rashi is answering the question: “Doublefold of all that he possesses” implies doublefold of everything he possesses, i.e. that he should have two portions. [For example,] if he left three manah and there were five brothers, the firstborn should take two manah and the four [remaining] brothers should take one [manah]! Rashi answers that “of all he possesses” does not refer to “doublefold” but means as follows: “Doublefold [of one brother’s share],’ i.e., the equivalent of what two brothers [take].” And [the term] “of all that he possesses” is a separate phrase.