Charles Ellicott Commentary Numbers 14:34

"After the number of the days in which ye spied out the land, even forty days, for every day a year, shall ye bear your iniquities, even forty years, and ye shall know my alienation." — Numbers 14:34 (ASV)

Even forty days, each day for a year.— The numbering recorded in chapter 26 took place after the death of Aaron, which happened on the first day of the fifth month of the fortieth year after the exodus (Numbers 33:38). Therefore, it follows that the year and a half that had elapsed since the exodus must be included in the forty years of shepherd life in the wilderness.

My breach of promise.— The noun rendered in this way occurs only in one other place, namely, Job 33:10. The cognate verb, however, occurs several times in this book in the sense of refuse, disallow, or hinder. (Numbers 30:8; Numbers 30:11; Numbers 32:7.) The meaning here appears to be rejection or alienation.