What is the first sin committed by the David in the episode with Bathsheba?

The first sin committed by King David in the episode with Bathsheba is his lustful desire for her. While he was supposed to be leading his army in battle, he instead stayed behind in Jerusalem, where he saw Bathsheba bathing and was captivated by her beauty. This led him to summon her to his palace, resulting in adultery and the subsequent set of events that included deception and murder to cover up his actions.