Plenteous Redemption

Why was David in such great distress when he wrote this Psalm? What hope is there for distressed sinners? What does 'mercy' mean? What does 'grace' mean? Why is 'redemption' such a glorious Word? How did God satisfy His Justice and still redeem the people He chose to save? Who is the Redeemer and why did the Redeemer have to be God's Son? Why are all those that boast of being saved by their heritage or birth still in darkness and ignorance? Where does sin come from and how does it affect the world with it's dire consequences? Why is it important to realize the debt of sin within yourself? Why is it a deadly mistake to think that God could stand by and allow sinners to go unpunished? Outside of Christ the Redeemer can God the Father accept any prayer or will that prayer actually condemn that person?