Some people think that truly good and righteous people are just born that
way, and that the rest of us can only hope to avoid doing harm, at best.
But that's clearly not Rambam's (or our own) perspective on things, as he
asserts that we *all* have what it takes to achieve spiritual excellence
in this world.
Understand, though, that that wasn't always as self-evident as it seems.
In the past many thinkers contended that certain people were
born "heroes", as they called them, who could do no wrong, while the rest
of us are doomed to shlep along in our clumsy, often less-than-righteous
ways. In point of fact, that argument is still very much alive today, with
some claiming that we're each genetically "wired" to be one way or the
other, without much free will ... but that's not the point here.
There's something else many thought in the past: it's that "when a person
who subdues his yetzer harah does lofty things", that is, if a person
struggles with his urge to do something wrong and manages to stave off the
temptation and to do good instead, he's nonetheless "not so praiseworthy".
Why? Because he'd still be "longing and yearning to do bad". They'd grant
you that "he'd struggled with his longings" and managed to "withstand the
promptings of his personal bents, desires, and disposition", but their
point would be that he'd be "suffering in the process", that it wouldn't
come naturally to him, so he wouldn't be all that noble.
The so-called hero or eminent, sinless person would be loftier and more
perfect than the one who subdues his yetzer harah, simply because the
latter "still longs to do something bad" which indicates "an inherently
bad disposition" on his part -- even though he hadn't succumbed.
Their contention was that if you or I were "really" good, we wouldn't even
*think* of sinning. And that struggling not to sin, and even managing to
be successful at that, wouldn't be all that great.