כי לא דבר רק הוא מכם. לֹא לְחִנָּם אַתֶּם יְגֵעִים בָּהּ, כִּי הַרְבֵּה שָׂכָר תָּלוּי בָּהּ, כי הוא חייכם; דָּ"אַ — אֵין לְךָ דָבָר רֵיקָן בַּתּוֹרָה שֶׁאִם תִּדְרְשֶׁנּוּ שֶׁאֵין בּוֹ מַתַּן שָׂכָר, תֵּדַע לְךָ שֶׁכֵּן אָמְרוּ חֲכָמִים "וַאֲחוֹת לוֹטָן תִּמְנָע" (בראשית ל"ו) "וְתִמְנַע הָיְתָה פִילֶגֶשׁ וְגוֹ'", לְפִי שֶׁאָמְרָה אֵינִי כְדַאי לִהְיוֹת לוֹ אִשָּׁה הַלְוַאי וְאֶהְיֶה פִילַגְשׁוֹ, וְכָל כָּךְ לָמָּה? לְהוֹדִיעַ שִׁבְחוֹ שֶׁל אַבְרָהָם שֶׁהָיוּ שִׁלְטוֹנִים וּמְלָכִים מִתְאַוִּים לִדַּבֵּק בְּזַרְעוֹ (ספרי): כי לא דבר רק הוא מכם FOR IT IS NOT A VAIN THING FOR YOU — it is not for nothing that you are to occupy yourselves laboriously with it. because much reward depends on it, כי הוא חייכם FOR IT IS YOUR LIFE (life is the reward). Another explanation: There is not one empty (ריק i.e., apparently superfluous) word in the Torah that, if you properly expound it, has not a grant of reward attached to it for doing so. You can know this, for so did our Rabbis say: It states (Genesis 36:22) “And Lotan’s sister was Timna”; (Genesis 36:32) “and Timna was concubine [to Eliphaz, Esau’s son]”. Why is this stated? Because she (Timna) said, “If I am unworthy to become his (Elphaz's) wife, would that I would become his concubine!”. And why all this (why does Scripture enter into all these details of her birth and marriage; of what interest is it to us)? To tell you in what distinction Abraham was held — that rulers and kings (Lotan was one of the chieftains of Seir, cf. Genesis 36:20—21) were eager to connect themselves by marriage to his descendants (Sifrei Devarim 336:1; cf. Rashi on Genesis 36:12).