I Will Protect This City and Save It for My Own Sake

Hezekiah, a descendant of David under the terms of the covenant, is doing his part. The emperor comes to the rescue and delivers his vassal and his people. So when Jacob says of Nephi that he's a king and protector, it's not necessarily the proxy Savior himself who does the actual protecting or delivering. It's really the Lord,. but what he can do is qualify the Lord's people for deliverance.