Musar sur Josué 1:2

We are dealing with a Divine decree that was issued already prior to this incident, but the execution of which had been delayed pending certain actions by the human beings to whom it was to apply. The decree concerned the coming into being of the kingdom of David and all that this entailed. A single error of Saul sufficed to trigger its execution, whereas on the other hand when David committed several sins, this did not have fatal consequences for his dynasty (compare the discussion in Yuma 22b). What occurred here, was of a similar nature. G–d told Moses already in Exodus 6,1, after the latter had complained that his mission had resulted in additional hardships for the people he had been sent to liberate, עתה תראה, now you will see!" Sanhedrin 111, comments on this that it had already then been decreed that Moses would not lead the Jewish people into the Holy Land, that he would only experience the deliverance of the people from Egypt. A similar decree existed due to the conduct of the people, i.e. that that generation also would not see the Holy Land. This was because they did not deserve all the miracles that would be performed for them at the time of their entering the Holy Land. Had Moses led them then, the miracles he would have performed would have outclassed those performed when Joshua defeated the thirty-one kings, and the people simply would not have deserved such miracles. The Ralbag explains all this in connection with Joshua, 1,2, when G–d told Joshua: "My servant Moses has died, and now arise and cross this river Jordan!"