Based on how the stage directions are used in this excerpt from act i, scene i of richard iii, what is likely the main purpose of providing stage directions in a drama?

(alarum. enter king richard iii and richmond; they fight. king richard iii is slain. retreat and flourish. re-enter richmond, derby bearing the crown, with divers other lords)

richmond (henry vii): god and your arms be praised, victorious friends,
the day is ours, the bloody dog is dead.

sir william stanley. courageous richmond, well hast thou acquit thee.
lo, here, this long-usurped royalty
from the dead temples of this bloody wretch
have i pluck'd off, to grace thy brows withal:
wear it, enjoy it, and make much of it.