Why does Genesis 22:7 say "אַבְרָהָם אָבִיו" rather than just "אַבְרָהָם" or "אָבִיו"? It's redundant.
(My kid's question.)
The text is not just dispassionately telling a story. Each word is pregnant with meaning. That is why the initial command was קַח-נָא אֶת-בִּנְךָ אֶת-יְחִידְךָ אֲשֶׁר-אָהַבְתָּ, אֶת-יִצְחָק, 'Take now thy son, thine only son, whom thou lovest, even Isaac'.
Here, the innocent child is turning to his father, whom he trusts, and asking this question. This also establishes parity in preparation for וַיֵּלְכוּ שְׁנֵיהֶם יַחְדָּו.
Such dramatic emphasis is also present in the unnecessary repetitions of וַיִּשָּׂא אַבְרָהָם אֶת-עֵינָיו וַיַּרְא וְהִנֵּה, among many other examples.
Also, otherwise the Torah Codes would be off. ;)
This seems to be addressed by the Midrash:
Bereishit Rabbah Parshah 56
הה"ד ויאמר יצחק אל אברהם אביו אבי למה אבי אבי ב' פעמים כדי שיתמלא עליו רחמים
This is why it is written and Isaac said to Abraham his father: "my father". Why "my father" "my father" twice? In order to fill him with mercy.
The wording of this seems slightly odd as it cites the verse as אביו אבי but then interprets it as אבי אבי. R. Chanoch Zundel in his commentary there apparently explains that the verse referring to Abraham as "his father" is indicative of Isaac calling him "my father", in which case the explicit mention of "my father" means that Isaac called Abraham "my father" a second time:
שפי' ויאמר יצחק אל אברהם אביו שקרא יצחק לאברהם אבי ועוד אמר אבי
It is interpreting and Isaac said to Abraham his father [as meaning] that Isaac called Abraham "my father", and [then] he again said "my father".
Other versions of the Midrash have slightly different wordings, which may make it easier to read. The critical edition by Albeck (p.599) has:
למה אביו אבי
This makes it more clear that the Midrash is considering the reference to Abraham as "his father" redundant to Isaac's reference to Abraham as "my father".
The Zecher Chanoch edition has it as:
הדא הוא דכתיב ויאמר יצחק אל אברהם אבי אבי
This makes it sound like the verse itself had Isaac saying "my father twice". This could itself be a mistake, it may be something along the lines of R. Zundel's explanation, or it may be indicative of a textual variant in the verse itself.
In any case, the point of all this seems to be that the reference to Abraham as "his father" somehow reflects Isaac's plea for mercy.