Now, “don’t be surprised by the fact that some personal failings would lessen the quality of one’s prophecy” Rambam offers, since “some character flaws — like anger — actually withheld it”, he points out.
The crux of the matter is that while each failing acted as a “screen” or impediment to G-d’s Presence, some proved to be so excessive, such instances of personal imbalance, that they acted as out-and-out obstacles to it. One such trait was anger — which is understandable, since angry people can’t be trusted to convey what they’d been told truthfully, as their anger would undoubtedly color their understanding.
But there were other traits that would act that way, too. Rambam mentions worry and anxiety specifically. After all, our forefather Jacob’s Divine inspiration left him while he mourned for (i.e., worried about) Joseph‚ after the latter was brought to Egypt.
Understand of course that someone who’d always be angry or worrisome couldn’t be a prophet in the first place, since he wouldn’t be the sort of even-tempered and emotionally healthy person that Rambam said a prophet would have to be.
Nonetheless the point for us is that while we’re not prophets, so G-d’s full Presence is more often closed off from us than not, we too could allow Him into our lives more so if we’d improve our characters. And given that our main thrust in life is to comprehend G-d Almighty as much as a human being can, as we were told in Ch. 5, it stands to reason that rectifying our characters is essential to our achieving spiritual excellence.