Well, I would certainly disagree that the whole story is a metaphor for our journey through life. Instead, I take it as historical narrative.

In Deuteronomy 32.51, Moses is told by God why he's not allowed to enter the Promised Land, despite his long walk, and is to die on the doorstep. "This is because both of you broke faith with me in the presence of the Israelites...and because you did not uphold my holiness..." It's a specific reference to Numbers 20.10-11, where Moses disobeyed God. But there's more to it.

The comments in Numbers 20 indicate that, in general, Moses was guilty (at least to some extent) of the same rebellious attitude against God that characterized all the people who were not permitted to enter the Promised Land. In Numbers 20.10, he accuses the people of being rebellious, but then hypocritically, he acts as a rebel himself by striking the rock. He is motivated by anger and frustration (the complaint motif) just like the people are. He fails to bring glory to God, just like the people. He doesn't show full trust in God, just like the people. He fails to display humility, just like the people. Etc. Etc.

In essence, sadly, Moses becomes somewhat the archetype of the rebellious generation, and his act of striking the rock is the straw that defined it (just as Adam and Eve eating the fruit was theirs). His sin by striking the rock was a glaring example of all that was wrong with the "sinful generation" that was not allowed to enter the Promised Land, and therefore Moses was not allowed to enter either.

Because you've spent the last 3-4 books reading about this guy and his long journey through life, the desert and everything in between and getting to the promised land is the overarching goal and then he gets there (if you look at a map the mountaintop on which he dies is in the promised land, but only on the outskirts and its not the best in terms of resources) and bloody dies. Its like walking from Mongolia to get to Buckingham Palace with 50000 people in tow and getting there but then dying on the doorstep. Like, you all risked everything for this. This was your life. And then you just die.
And he's pretty chill with it (???). And its premeditated for legit no reason. And it's so frustrating.

Doesn't exactly help I view the whole story as a metaphor for our journey through life and its like... Does anyone get there? Really? Urgh, it bugs me writing this.