What you think about God is so important.  How you see God determines the kind of prayers you pray.  If you see God as busy, then you will only pray once in a while because you don’t want to bother Him.  If you see God as disinterested then you will be hesitant to come to Him with your requests.  If you see Him as stingy then you may ask for something big but offer to not ask for anything again to balance out the request.  The Apostle Paul saw God as exceedingly powerful and generous, as evidenced by the first three chapters of this book, and this emboldened him to pray big prayers.