GEN815 We are obligated to do all we can to sve someone who is held captive. The Torah goes into detail about the war of the four kings against the five kings in order to show us how much Abraham exerted himself in his effort to save the captive Lot.  This was a fulfillment of the commandment to save a person whose life is in danger (see Leviticus 19:16). Although Lot had only himself to blame for choosing to dwell in Sodom amongst wicked inhabitants, Abraham did all he could to save him.  Ahavas Chesed, Introduction.  The Ramban points out that it probably took Abraham a long time to reach Lot and free him, because the distance he traveled was great.  From this we learn that we must try to free someone from captivity, no matter how much time it entails.  PLYN 48-49