The Midrash thinks that this was a great achievement on the patriarch’s part and showed how God-fearing he was (Gen. R. 43).
With respect, one might put it rather lower than that and say that a family member was in trouble and another member of the family had to do something about it.
Where is the evidence that a mission to get Lot back was a mark of reverence for God?
There is an answer in the Midrash itself: when a God-fearing person hears bad news, nachon libbo – their heart is firm and there is no panic or running away. Nor is there any complaining about their lot, no saying, “It isn’t fair, why me?… I can never win, nothing ever goes my way!”
It may not be fair, but something urgent has to be done. The philosophical discussion can be left for later.
In Abraham’s case, if he reacted to the news about Lot’s capture by sitting and moaning, Lot could be lost for ever. Tzaddikim do not waste precious time. They get on with the mitzvah.
Is that why it says in Ashrei, tzaddik HaShem b’chol d’rachav, “The tzaddik has HaShem in all His ways”?