Who is the Man After God's Own Heart?

Why is it that many don't see what the sin of Saul was? Why was it ordained that Adam and Saul should fall? Why did all those that served as Old Testament types of Christ have to fail? Does anyone have the power to truly put God first in their life? Who alone is pleasing to God in service? How is every child of Adam either of Abel or of Cain when it comes to salvation? Is any heart more evil than another among the children of men? Does anyone seek God with all their heart as God requires? What did God mean by 'begotten'?