כִּ֣י תִשְׁמַ֗ע בְּקוֹל֙ יְהוָ֣ה אֱלֹהֶ֔יךָ לִשְׁמֹר֙ אֶת־כָּל־מִצְוֺתָ֔יו אֲשֶׁ֛ר אָנֹכִ֥י מְצַוְּךָ֖ הַיּ֑וֹם לַעֲשׂוֹת֙ הַיָּשָׁ֔ר בְּעֵינֵ֖י יְהוָ֥ה אֱלֹהֶֽיךָ׃ (ס)
когда будешь внимать голосу Господа, Бога твоего, соблюдать все заповеди Его, которые Я заповедую тебе сегодня, исполнять то, что прямо в глазах Господа, Бога твоего.
Ibn Ezra
The verse for you will follow… means: So will you do, if you seek to practice what is right in His eyes. This passage is juxtaposed to the subsequent passage on account of the enticers to idolatry (be they brother, or son, or father, or the inhabitants of the “seduced city”) — it is forbidden to mourn over them at all, and certainly to cut one’s flesh, which is forbidden for any dead person.
Sifrei Devarim
(Ibid. 19) "when you hearken to the voice of the L-rd your G-d to keep…": From here they said: If a man begins to hear a little, in the end, he merits hearing much. If he begins to hear, in the end he keeps.
Sifrei Devarim
"to keep all of His mitzvoth that I command you this day": that a "slight" mitzvah be as beloved by you as a "weighty" one.