Verse 18: Whosoever he be that doth rebel against thy commandment, and will not hearken unto thy words in all that thou commandest him, he shall be put to death: only be strong and of a good courage.
[Whosoever doth contradict thy mouth, אֲשֶׁר־יַמְרֶ֣ה אֶת־פִּ֗יךָ] Whosoever doth rebel with respect to thy mouth (Montanus, Drusius, Vatablus), that is, thy speech (Drusius), thy word (Masius), thy commandment (Arabic, similarly Junius and Tremellius), against thy word (Jonathan).
[Whosoever doth contradict…and not obey] That is, contumaciously. This law pertains to the King of the Hebrews. Whosoever is condemned by this law, is said among the Hebrews to be condemned for the sake of the kingdom; just as among the Romans, for the sake of Majesty. In the case of this one crime, goods were confiscated, 2 Samuel 9:7; 1 Kings 21:14, 15. But it is remarkable that Kings under the pretense of prevention judged concerning this crime pertaining to the injury of Kings, as much as Public Judges; as appears in 1 Kings 2:29, etc., and there it is noted by Levi Ben Gershon and Kimchi. Such was the estimation of the Hebrews concerning the uprightness of their Kings (Grotius). Other translate it, whosoever shall alter thy mouth (certain interpreters in Drusius, Malvenda), that is, shall pervert thy word by speaking or doing otherwise than thou hast prescribed (Malvenda).
In all that thou commandest him, not repugnant to God’s commands; for none can be so foolish to think, that if he had commanded the people to blaspheme God, or worship idols, the people were obliged to obey him therein.
[Only wax thou strong] Either it is a prayer, or an exhortation: that is to say, Only let thou be of a strong and confident soul; in us thou shalt lack nothing. Rabbi Levi thus: Only that thou mightest be strong and resolute in administrating the kingdom according to the prescriptions of the Law (Masius).
 Hebrew: כָּל־אִ֞ישׁ אֲשֶׁר־יַמְרֶ֣ה אֶת־פִּ֗יךָ וְלֹֽא־יִשְׁמַ֧ע אֶת־דְּבָרֶ֛יךָ לְכֹ֥ל אֲשֶׁר־תְּצַוֶּ֖נּוּ יוּמָ֑ת רַ֖ק חֲזַ֥ק וֶאֱמָֽץ׃
 מָרָה signifies to rebel.