||Do not worship God your Lord with such practices. In worshiping their gods, [these nations], committed all sorts of perversions hated by God. They would even burn their sons and daughters in fire as a means of worshiping their gods!
Lo-ta'aseh chen l'Adonay Eloheycha ki chol-toavat Adonay asher sane asu l'eloheyhem ki gam et-bneyhem ve'et-benoteyhem yisrefu va'esh l'eloheyhem.
||[It is enough that you] carefully observe everything that I am prescribing to you. Do not add to it and do not subtract from it.
Et kol-hadavar asher anochi metsaveh etchem oto tishmeru la'asot lo-tosef alav velo tigra mimenu.
|Do not worship...|
(Ibn Ezra; Ramban; Bachya). Literally, 'Do not do this to God your Lord;' see Deuteronomy 12:4.
|Do not add...|
This is a commandment not to add or subtract from any observance prescribed by the Torah (Rashi; Sifri; Sefer HaMitzvoth, Negative 313). There is also a commandment not to try to increase or diminish the number of commandments (Deuteronomy 4:2; Adereth Eliahu; HaKethav VeHaKabbalah). In simplest terms, the Torah here is saying that we should not try to 'improve' the Torah by borrowing gentile practices.