ובדבר הזה אינכם מאמינים, "In this matter you did not believe in God, etc.⁠" Why did Moses have to say: "in this matter?⁠" Rashi understands Moses' words as a reference to God's promise that the people would enter the land of Canaan. This does not appear acceptable. I believe the plain meaning of the verse is that Moses referred to the miracles God had demonstrated when He lifted the whole Jewish people out of Egypt just as a father carries his son. They did not even believe the miracles they themselves had experienced (Exodus 14,19 compare Rashi there) which Moses recalled in verse 31. Proof that the Israelites were lacking in faith at the time is provided by Exodus 17,7 "If the Lord is in our midst or not?⁠" The Zohar on that verse provided us with the well known parable of the father who carried his son on his shoulder. When they met someone, the son asked the stranger if he had seen his father. Israel's question in the verse we referred to is compared to the effrontery of the child in the parable by the Zohar. This then is what Moses referred to with the words: "in this matter you did not have faith in the Lord your God.⁠" Moses added: "who is walking before you, etc,⁠" in order to underline that in view of the continued miracles performed constantly by God there was no excuse for this lack of faith.