The story of David is as follows:  The tribes of Israel were fragmented, so they prayed to have a King of all of Israel.  God spoke to the Prophet Samuel to say that Saul was to be king.  Samuel then annointed Saul king and told Saul that if he obeys the commandements of God, his Kingdom will be established and his house will last forever.  Saul then mostly listened to God’s commandements, had great successes, but he didn’t follow the commandements exactly for what seemed to him to be valid reasons.  Seeing that Saul could not obey perfectly, God withdrew his support of Saul and told Samuel to annoint another.  Saul remained King, though, as there was noone to depose him.  God told Samuel to annoint a small shepherd boy named David as King.  David was very dedicated to God and sincere of heart, and so God saw within him the qualities of being a King.  Not saying he was the new annointed one, David went to Saul and joined his army to serve.  When the giant Goliath was terrorizing the countryside, even though David was still just a boy, he managed to kill Goliath with his sling shot.  David then became very famous with the army and led them to many victories.  Saul came to realize that David was God’s new chosen King, became jealous, and even though David never did anything against Saul, Saul plotted to have David killed.  David escaped, the army proved loyal to David, and Saul and his supporters were eventually wiped out by the Philistines.  The crown then came to David.

David then captured Jeruselem without destroying it (by cutting off its water).  In Jeurselem, David fell in love with a woman who was the wife of one of his soldiers, got her pregnant, and then when he couldn’t cover it up had the soldier sent to where he would surely die in battle.  Nathanial, the prophet after Samuel, told David that God was very displeased, their child would die and evil would rise up in David’s house.  Later, one of David’s sons raped one of his daughters, and David banished him but did not kill him because he said the covenant between a father and son prevents such things.  Another son thought David was weak for not killing the rapist, so he did so instead.  David then banished that son, who subsequently plotted to take over in a coup.  Realizing he was outnumbered, instead of fighting him and Jeruselem being destroyed, David left Jeruselem to go find supporters.  He crossed the Jordon river, found supporters and waited for the usurper son to come and get him.  David’s army then defeated them and David returned to Jeruselem.  David’s dream had always been to build a temple for the Arc of the Covenant, but God said that David had spilt too much blood in his life to build the temple, but that his son Solomon would do so. 

How can we understand this story from a Kadampa perspective:

1. Our success in our endeavors is entirely dependent upon how fully we accomplish all of our deeds through total reliance upon the divine.  With perfect faithful reliance, all of our actions will be perfect because they are inspired by omniscience and blessed by all of the holy beings.  Any deviation from this, and things will quickly fall apart as they did for Saul. 
2. Through faithful reliance, even small boys can accomplish anything and rise to be a king.  David was not some massive warrior, but instead a scrawny boy, yet despite this he defeated Goliath and became a great general.  He would say all through the power of reliance.
3. David had no ill intent towards Saul, and in fact helped him in every way he could.  First by dispelling some demons with his harp playing and by telling Saul the prayer of “The Lord is my Shepherd.”  This is a magnificint prayer.  David did not plot to get the crown, rather he simply proved himself, Saul lost the crown and it came to David.  This is an important example because many people can quickly become spiritually ambitious within religious institutions and plot to take over for what they feel to be valid reasons.  But a true leader serves others, and through that service naturally becomes a leader through being given leadership. 
4. Once David became King, he lost his way and committed adultry and murder.  This cost him dearly.  In the Bible it is presented as punishment, but from a Kadampa perspective this is just how karma works.  Negative minds and negative actions activate negative karmic seeds on our mind, which ripen in the form of suffering.  There is no external being punishing us, but it is still a fairly accurate metaphor for describing what seems to be the dynamic.  It was only by returning to be true to God that David eventually won his crown back.
5. If our motivation is completely pure, then even if we engage in what would normally be considered very negative actions we do not accumulate negative karma.  The time of David must have been a brutal time, and to survive required defeating those who wanted to destroy you.  David had to kill many people, either directly or indirectly, but his motivation was following purely the word of God for the sake of building a Kingdom and home for God in Jeruselem.  As such, his extensive actions of killing in the name of building the Kingdom were apparently not negative.  But when he selfishly stole a man’s wife and had him killed, this was purely negative and resulted in great suffering.  It is the same in the Dharma.  If our motivation and faith are genuine and pure, it is sometimes necessary to engage in what would otherwise be negative actions, but these actions will not in fact be negative but will be pure.  For example, when a previous incarnation of Buddha Shakyamuni killed the one sailor to save the 100 others.  But we need to be very careful with this that we don’t use it as an excuse to rationalize our negativity.
6. Even though it was his dream to do so, David could not build the temple because of all that he had done.  But he did create the conditions for it to happen and his son was able to do so.  This is not unlike Moses who was able to bring his people to the promised land, but not enter it himself.  There is a powerful lesson in this, namely to not do what is right for reward in this life because that makes our actions worldly.  We should be happy for others to get the glory and instead be happy for ourselves to do the hard work that nobody else can do.