In Macbeth, why does Macbeth keep fighting in the final scene even once he knows the prophecies have come true and it is time for him to die?

The scene you want to analyse is Act V scene 8. This is
when Macbeth confronts Macduff in his castle and Macduff tells him that he was "untimely
ripped" from his mother's womb, meaning that he is not "of woman born" and thus can kill
Macbeth. The final speech of Macbeth is particularly interesting to examine, and it can
be used to argue that in this final scene, we have to reevaluate the character of
Macbeth and to a certain extent he reclaims some of his nobility and honour in the way
that he meets his death. Note what he says:

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I will not yield

To
kiss the ground before young Malcom's feet,

And to be
baited with the rabble's curse.

Thought Birnam wood be come
to Dunsinane,

And thou oppos'd, being of no woman
born,

Yet I will try the last: before my
body

I throw my warlike shield: lay on,
Macduff;

And damn'd be him that first cries, "Hold,
enough!"

These final words
and the way in which Macbeth chooses to not accept the cruel fate that destiny and the
witches have planned for him meekly bestows a certain amount of dignity upon his ending.
Whatever the forces that are ranged against him, and however impossible his situation
is, Macbeth is a character who refuses to yield without using all of his strength and
might to fight against fate and destiny. Even though he recognises his time is up, his
action of continuing to resist makes him a character that we come to respect. Macbeth
thus keeps on fighting because it is not in his nature to give in without a struggle. He
is a brave and volorous individual, whatever else we may think of
him.