Shalom and thank you for your question!
Why would an uncle sacrifice his life for his nephew? Why indeed…
It sems you are referring to the incident of Abraham, forefather of the Jewish people, going to fight the evil kings in order to save his nephew Lot, with the support of G-d’s miracles and his faithful servant Eliezer. (On a Kabbalistic level, the evil kings represented intense forces of impurity which Abraham was to conquer with his purity and righteousness.)
Before discussing this in more detail , I would just like to ask… have you heard of people who gave up their lives for their principles? It could be principles which are just a matter of pride, like when brave knights fought over a fair maiden and the one who remained alive received the maiden’s hand in marriage, and it could be a religious principle. People will risk their lives to be the first to climb the highest mountain or trek the most dangerous trek. It could also be a scientific discovery for which a person is willing to give up, if not their life, at least their comfort for… In many of these cases, the ego is involved, but true self sacrifice is when the motivating factor is truly altruistic. Belief in a higher goal is the motivating factor…
In the realm of Torah outlook, Abraham was the righteous leader of the generation and as such, excelled in humility and kindness. Therefore it was natural to reach out to help his nephew. Moreover, he had a debt of gratitude towards Lot. When Abraham had to go down to Egypt because of famine, and was afraid they would kill him in order to take his beautiful wife, (even though their culture was promiscuous the Egyptians of the time would not take a living man’s wife,) Lot closed his mouth when Abraham claimed Sarah was his sister and did not disclose the truth.
Finally, redeeming captives takes top priority in Jewish law and outlook. It is even considered greater than the all- encompassing Mitzvah of charity, (Tzedaka)!
Over the generations many righteous people have gone to extreme lengths to redeem captives, whether it involved raising humungous sums of money to pay ransom, fighting mighty opponents, or other means.
We can learn much from this story, in terms of a shining example of family values and altruism…
