4:1ד׳:א׳
1 א

והאדם ידע. כְּבָר קֹדֶם הָעִנְיָן שֶׁל מַעְלָה, קֹדֶם שֶׁחָטָא וְנִטְרַד מִגַּן עֵדֶן, וְכֵן הַהֵרָיוֹן וְהַלֵּדָה, שֶׁאִם כָּתַב וַיֵּדַע אָדָם, נִשְׁמָע שֶׁלְּאַחַר שֶׁנִּטְרַד הָיוּ לוֹ בָנִים:

(1) והאדם ידע AND THE MAN KNEW already before the events related above took place — before he sinned and was driven out of the Garden of Eden. So, also, the conception and birth of Cain took place before this. Had it been written, וידע אדם it would imply that after he was driven out children were born to him (Genesis Rabbah 22:2).

2 ב

קין. עַל שֵׁם קָנִיתִי:

קין — She called him so with reference to her use of the word.

3 ג

את ה'. כְּמוֹ עִם ה', כְּשֶׁבָּרָא אוֹתִי וְאֶת אִישִׁי, הוּא לְבַדּוֹ בְּרָאָנוּ אֲבָל בָּזֶה שֻׁתָּפִים אָנוּ עִמּוֹ (נדה ל"א):

ה‘ — ;את קניתי is like ‘עם ה “with the Lord”; she meant to say: when He created me and my husband He created us by Himself, but in the case of this one we are copartners with Him (cf. Niddah 31a).

4 ד

את קין את אחיו את הבל. ג' אֶתִים רִבּוּיִים הֵם, מְלַמֵּד, שֶׁתְּאוֹמָה נוֹלְדָה עִם קַיִן, וְעִם הֶבֶל נוֹלְדוּ שְׁתַּיִם, לְכָךְ נֶאֱמַר וַתֹּסֶף (בראשית רבה):

את קין… את אחיו את הבל —The threefold ‘את’ signify extension of the scope of the text, teaching that a twin sister was born with Cain, and that with Abel two were born; consequently the text states ותוסף “and she bore more’’ than the previous time (Genesis Rabbah 22:3).