John Gill Commentary Deuteronomy 32:51

"because ye trespassed against me in the midst of the children of Israel at the waters of Meribah of Kadesh, in the wilderness of Zin; because ye sanctified me not in the midst of the children of Israel." — Deuteronomy 32:51 (ASV)

Because you trespassed against me among the children of
Israel
By their unbelief, doubting whether God would give water or no to such a rebellious people, and by giving way to passion and wrathful expressions: and this was done

at the waters of Meribahkadesh ;
so called, to distinguish it from another Meribah, where also there was a contention on account of water, (Numbers 20:13) (27:14) :

in the wilderness of Zin ;
where Kadesh was, and further describes and distinguishes this place; of the one we read in (Exodus 17:7) ; and of the other, which is here referred to, in (Numbers 20:1Numbers 20:13) ;

because you sanctified me not in, the midst of the children of Israel ;
through their unbelief and disagreeable behaviour, they sanctified him not themselves, and gave no honour to him, nor were the cause of his being sanctified by the Israelites; and this was the reason why Moses and Aaron might not enter into the land of Canaan, (Numbers 20:12) (27:12-14) .