Verse 9

and then you are careful to observe all these commandments I am giving you today(namely, to love the LORD your God and to always walk in his ways), then you must add three more cities to these three.

Referenced Verses

• Josh 20:7-8 : 7 So they selected Kedesh in Galilee in the hill country of Naphtali, Shechem in the hill country of Ephraim, and Kiriath Arba(that is, Hebron) in the hill country of Judah. 8 Beyond the Jordan east of Jericho they selected Bezer in the wilderness on the plain belonging to the tribe of Reuben, Ramoth in Gilead belonging to the tribe of Gad, and Golan in Bashan belonging to the tribe of Manasseh.
• Deut 11:22-25 : 22 For if you carefully observe all of these commandments I am giving you and love the LORD your God, live according to his standards, and remain loyal to him, 23 then he will drive out all these nations ahead of you, and you will dispossess nations greater and stronger than you. 24 Every place you set your foot will be yours; your border will extend from the desert to Lebanon and from the River(that is, the Euphrates) as far as the Mediterranean Sea. 25 Nobody will be able to resist you; the LORD your God will spread the fear and terror of you over the whole land on which you walk, just as he promised you.
• Deut 12:32 : 32 Idolatry and False Prophets(13:1) You must be careful to do everything I am commanding you. Do not add to it or subtract from it!