(Read Esther 8:1-2)

What Haman would have done mischief with, Esther will do good with. All the trust the king had reposed in Haman, he now placed in Mordecai: a happy change. See the vanity of laying up treasure upon earth; he that heapeth up riches, knoweth not who shall gather them. With what little pleasure, nay, with what constant vexation, would Haman have looked upon his estate, if he could have foreseen that Mordecai, the man he hated above all men in the world, should have rule over all that wherein he had laboured! It is our interest to make sure of those riches which will not be left behind, but which will go with us to another world.

For a more detailed summary select the link below.

Esther 8 Bible Commentary – Matthew Henry (concise) (christianity.com)

Esther 8:2

² The king took off his ring, which he had taken from Haman, and gave it to Mordecai. Esther set Mordecai over the house of Haman.