I found this to give some background (here) to the deep rivalry that existed between Mordecai and Haman:
To think that if Saul had obeyed that Haman would have never been born makes for an interesting side story. Disobedience always has consequences. Not obeying your parents has consequences. Not listening to teachers, leaders, and bosses has consequences. Not following God has far reaching consequences that go way beyond what Saul could have imagined when he chose to spare some of the lives of the Amalekites. Even when we obey something half way instead of all the way, there are consequences. There are consequences when we don't play by the rules.
MacArthur compares the book of Esther to a game:
God keeps his promises. He uses what we are, meets us where we are, and accomplishes what he said he would. May our focus be on obedience to what God desires for us so that we can be willing instruments to His plan.
This verse from the NT also stood out for me:
So many things get in the way for me and my walk with God. What I need to remember is that where I put my time and my energy is where my heart will be. My prayer is that I will willingly submit to obedience when God calls me to do things that make me uncomfortable...just like Esther was called to do.
Tomorrow's Bible In a Year Passage passage: Esther 6-8;