I think it shows our flawed human nature. We respond to what we see and feel, not what we know( the word, promises of God).I think we work things out in own mind to protect ourself and blame others, when we fall short. No the purpose is to show that God is faithful to His word, He does not change to his surrounding, He is not like us. God is faithful to every last word He has promised, I don't have to worry about it, He is more than trustworthy