כִּ֣י יְדַעְתִּ֗יו לְמַעַן֩ אֲשֶׁ֨ר יְצַוֶּ֜ה אֶת־בָּנָ֤יו וְאֶת־בֵּיתוֹ֙ אַחֲרָ֔יו וְשָֽׁמְרוּ֙ דֶּ֣רֶךְ יְהוָ֔ה לַעֲשׂ֥וֹת צְדָקָ֖ה וּמִשְׁפָּ֑ט לְמַ֗עַן הָבִ֤יא יְהוָה֙ עַל־אַבְרָהָ֔ם אֵ֥ת אֲשֶׁר־דִּבֶּ֖ר עָלָֽיו׃
For I have singled him out, that he may instruct his children that come after him, and his posterity to keep the way of the LORD by doing what is just and right, in order that the LORD may bring about for Abraham what He has promised him.”
In light of this verse, we have an automatic question of seemingly extra wording - 'his children that come after him'. Of course his children come after him, this word, Acharav, seems extra.
And it's possible to say, with the help of Heaven, to open up with what I said in regards to the day of passing of a known righteous individual, and why we made a celebration yearly on the anniversary of the day of passing (called Hilula in Hebrew).
As well, the source of calling this day a Hilula can be found and explained in the Holy Zohar.
דְּהָא חֲמֵינָא דְּכֻלְּהוּ חַדָּאן בְּהַאי הִלוּלָא דִּילִי, וְכֻלְּהוּ זְמִינִין
We also learn that the word Hilula is a word implying joy and happiness, as we see in the below Talmud..
אֲמַר לֵיהּ שְׁמוּאֵל לְרַב יְהוּדָה: שִׁינָּנָא, חֲטוֹף וֶאֱכוֹל חֲטוֹף וְאִישְׁתִּי, דְּעָלְמָא דְּאָזְלִינַן מִינֵּיהּ כְּהִלּוּלָא דָּמֵי.
Shmuel said to Rav Yehuda, his beloved student: Keen scholar, grab and eat, grab and drink, as the world from which we are departing is like a wedding feast
The reason there exists joy on the day of the passing of a righteous individual is as follows.. on this day, the Tzaddik traveled from one place where he was, to a much higher and lofty place, from one hall to another hall, which happens year after year. Therefore, we gather on this date every year and make a Seudat Mitzvah (a meal that counts as/based on a mitzvah/commandment), which is considered as such since this righteous soul is elevating on that day to an even higher level.
This is why it is very important that those that gather for the Hilula, are generally students of this individual, and in particular should be his family members. They should strengthen themselves in the service of HaShem, and accept upon themselves on that specific day to go in the ways and the path of straightness and goodness in order that they should connect to the righteousness of this individual and his good ways that he lived in. Through people elevating themselves accordingly on this day this soul becomes greatly elevated to higher and higher levels, and then once that happens the soul returns and imparts a great spiritual emanation onto us from the source of all blessings onto his children and students.
With this concept I explained what is written in the Talmud -
The implications here is that since while he was alive, Rabbi Yehuda HaNasi did many commandments and acts of kindness, and he was the leader of the Israel, and in general and specifically brought much good to the people.. but when a man dies, which is the way of the world for all humans, that soul becomes free from the obligation of Torah and commandments, as we see in the Talmud -
וְהַיְינוּ דְּאָמַר רַבִּי יוֹחָנָן, מַאי דִכְתִיב: ״בַּמֵּתִים חׇפְשִׁי״ — כֵּיוָן שֶׁמֵּת אָדָם נַעֲשֶׂה חׇפְשִׁי מִן הַתּוֹרָה וּמִן הַמִּצְוֹת.
When a person dies he then becomes free of Torah and mitzvot.
Therefore, now that Rabbi Yehuda was going to die, he called in his sons to tell them what he needs to happen, which was basically him saying that since he is going to the 'world of truth' (death) as all humans do, he will not be able to do the commandments anymore, and only what his sons and students do will give benefit to his soul.
With this we can explain what the sages have taught based on the statement in the Talmud that - 'The son is his fathers leg', which normally can be read that the son takes on the traits of the father, however we will see the deeper meaning here with this phrase.
שהבן כרעיה דאבוה הוא דקחשיב
A son is considered the legs of his father
Firstly, we have a question here, how can a son be considered the legs of his father? Dont we teach that sons next to their fathers are considered the center of the eye? (and not his legs). We shall answer, with the help of Heaven, that the importance of a man is not based solely on his actions, rather of those of his son/s as well.
If the sons of a man are blessed and righteous, even if the father was a simple man with nothing special going, the sons make the father an elevated, important and honorable man. This is not the case regarding a man whose sons are not praiseworthy, G-D forbid, even if the father is an elevated and important man, the lowly status of the son will decrease the status of the father.
As we know, the physical measure of a man is dependent on his legs. If the legs are long and large, the man will be considered a tall and larger person. Whoever has short legs, it will cause the man to be short. So therefore it makes sense that the sages can say that a mans sons is his legs, and the measure of the man himself!
This means to say that the mans sons are the measuring rod for the man himself!
This is why after a mans passing, his sons have the power to elevate the father from hall to hall. And regarding a scholar that passes away the sages of Israel say -
חָכָם שֶׁמֵּת — הַכֹּל קְרוֹבָיו. הַכֹּל קְרוֹבָיו סָלְקָא דַּעְתָּךְ?! אֶלָּא אֵימָא: הַכֹּל כִּקְרוֹבָיו, הַכֹּל קוֹרְעִין עָלָיו, הַכֹּל חוֹלְצִין עָלָיו, הַכֹּל מַבְרִין עָלָיו בָּרְחָבָה.
When a Torah scholar dies, everyone is his relative. The Gemara asks: Does it enter your mind that everyone is his relative? Rather, say: Everyone is considered to be like his relative, in the sense that everyone rends his garment in anguish over him, and everyone bares his shoulder over him in mourning, and everyone eats the mourner’s meal over him in the public square as mourners do. The death of a Torah scholar is a personal loss for every Jew.
If this is the case as we see above, we are all considered sons of a righteous scholar that passes away, and therefore it is incumbent upon all of us to be an aspect of the legs of a father, even with the righteous.
This can also explain the reason that while saying Yizkor during the holiday prayers (A special prayer only said by people who've experienced a loss), we send all the Jews outside (not included in the prayer) who still have his/her parents alive. To teach us that during the parents lifetime they don't need the acts of the children done on their behalf, because the parents can serve and perform commandments all on their own, and only after 120 years/death is the actions of the children needed for the elevation of the soul.
Now we can answer our first question, regarding the extra wording of 'Acharav', 'After him', which we already established was implied and not needed in the verse. The reasoning for this word is meanings to say Achar/after.. after what? After his death when he separates from us and is not able to anymore be in the world of judgement (Earth), and then his children preserve the path of HaShem, which is an act of charity and justice, as if to say that its considered charity/tzedaka for the deceased who cannot do for himself, and is now being elevated in Heaven.