Your sermon must explain how the kingship of Saul is a testimony to God’s mercy as well as God’s providence. In terms of application, you can focus on what it means to live with uncertainty and how we can trust God to be working things for our good, even if it does not seem to be the case at the moment.
1 There was a man of Benjamin whose name was Kish, the son of Abiel, son of Zeror, son of Becorath, son of Aphiah, a Benjaminite, a man of wealth.