Insecurity is a heart issue, not a mind issue. We use our minds to magnify what frightens us and we use it to make excuses why we are incapable, but the true source of our self perception is our heart. The Bible has told us our hearts are deceitful above all things and beyond cure and that they can become hard as stone and full of wickedness. Scripture says that it is out of the abundance of our hearts that our mouths speak. Not our literal muscle that pumps blood through our bodies, but the core of our lives that promotes our desires and longings. It motivates our decisions and actions. It is our hearts that tell us that we are the least; that we are lacking in some way; that we don't really have what it takes to succeed or even survive. Someone comes to you and gives you a compliment or wants to give you more responsibility, a promotion, and the first things that come to your mind are, "who did they choose first but said 'no'," or "they must not really know me," or "they must have me confused with someone else." When you realize that they really meant to ask you, that they really think well of you, then you begin the process of discounting yourself and your abilities, believing that you could never do it well enough.
Saul, the son of Kish, was a handsome man and taller than anyone else in Israel. Of him it was said "There is no one like him among all the people," yet when he first encountered Samuel, and Samuel told him of his place in the leadership of Israel, Saul said, much like Gideon, "But am I not a Benjaminite, from the smallest tribe of Israel, and is not my clan the least of all clans of the tribe of Benjamin? Why do you say such a thing to me?" He couldn't excuse his size, but he did excuse his lineage and their position of influence in the nation. You may say that was humility, and it is, a much needed quality in good leaders, but it is more than just humility. When the time came for Samuel to announce Saul as king, Saul was not present because he was hiding in the supply closet. That was after Samuel had said "The Spirit of the Lord will come powerfully upon you , and you will prophesy with them; and you be be changed into a different person. Once these signs are fulfilled, do whatever your hand finds to do, for God is with you." Unlike Gideon who checked and double checked to make sure it was God's plan, Saul went and hid from the responsibility. He knew what God wanted and knew the direction he was headed, but he was still afraid. I want you to read verse 9: "As Saul turned to leave Samuel, God changed Saul's heart, and all these signs were fulfilled that day." You saw it. What needed to change was not Saul's mind, but his heart. His core. How he saw himself in the light of God's providence and power.
It isn't about knowing more scripture or reading the newest book about changing the way we think. It is allowing God to transform our hearts. If our hearts are changed, then we will be different people. That doesn't mean that our insecurity goes away. It didn't with Saul, it won't with us. It does mean that we get our security not from how great we are, but from the One who is truly great. The God of the insecure.