Live

Everything has a weakness.
If you have no weakness--
if you are invincible --
then you are nothing.
And nothing can survive forever. I really don't think there's anything to change in this stanza.

Let's say that we are like candles. Get rid of the 'Let's say that'
Some take the highest risks
and challenge
the wildest odds for the pure thrill of it,
almost purposely trying to blow out
their flames. Others hide away in their homes,
afraid to be lit,
afraid to let their inner flame out.
In this stanza, you're first comparing the flame of a candle to life, am I right? ("almost purposely trying to blow out their flames). Then, you say that some candles hide away, afraid to be lit. If they aren't lit, they aren't alive, right? Maybe, instead of saying that, you could say how they're afraid to risk their flame

One day, your light I would say 'someday' instead of 'one day'.
will flicker from a raging fire to
a dull ember,
and you will leave into It's more than just leaving, though, isn't it? This half of the stanza doesn't have as much feeling as the rest of the poem, in my opinion.
the oblivious black of
death.

So, before you die,
make your weakness your strength.
Make your fire rage, your flame wave,
and your spark ignite. I don't really like this last line, it's been said many times before (usually for love, but still). Maybe say how strong the fire is: 'until your flame can be seen anywhere in the world' (also kind of comparing it to fame for doing something so amazing).

Whatever you look
to achieve in this life,
don’t let fear hold you back.

Chase your dreams.

Catch them.

Live.

So, before you die, make your weakness your strength. Make your fire rage, your flame wave, and your spark ignite.

Everything has a weakness. If you have no weakness, if you are invincible, then you are nothing. And nothing can survive forever.