It could be the result of a special training or encounter. For instance, he might have trained in a unique location filled with sand - based chakra, and over time, he learned to control it. Or perhaps he had an encounter with a powerful sand - controlling spirit that bestowed this ability upon him.
One possibility is that he inherits it through some sort of bloodline connection that was previously unknown. Maybe there's a distant relative who had the ability to control sand, and it somehow got passed down to Naruto.
It could be from some sort of ancient ninja training that was lost and he somehow discovers it. Maybe there's a hidden scroll or a hermit who teaches him this fire - controlling ability.
It could be a result of some new form of chakra manipulation. Maybe he discovers a way to combine wind and earth chakra in a unique way to create and control smoke.
One possible origin could be some kind of ancient bloodline. Maybe Naruto has a hidden bloodline that was passed down through generations and finally awakened, allowing him to summon angels. Another option is that he got this ability through a special training or a quest. He might have found a hidden place or an old sage who taught him the art of summoning angels.
One possibility could be some sort of new training he undergoes. Maybe he discovers a hidden jutsu scroll that teaches him how to control and produce fire from within his body. This could be a long - lost technique from an ancient ninja clan.
Well, in some fanfictions, Naruto's water - controlling ability could be a gift from a powerful sage. This sage, seeing Naruto's potential and his need for new powers to face upcoming threats, bestows upon him the ability to control water. Another origin could be that Naruto accidentally absorbs the chakra of a water - using enemy during a battle, and this chakra somehow melds with his own, giving him the power to control water.
One possibility is that it could be related to some ancient bloodline limit that was dormant in Naruto all along and somehow got activated. Another could be that he received some sort of special training or exposure to a unique chakra source that granted him this power.
The ability to control sand could be used for rescue operations. If someone is trapped under rubble or in a collapsed building, Harry could use the sand to carefully lift the debris without causing further harm. He could also use it for environmental control. For instance, if there's a drought - like situation, he could use the sand to create artificial rain clouds by using his magic on the sand's moisture content. Additionally, in battles, he could use the sand to blind his opponents by creating a sandstorm right in their faces.
He could use it for defense. For instance, creating a huge storm to block enemy attacks or a thick fog to hide his village from invaders.
It could be a result of some kind of rare genetic mutation. Maybe there was a dormant gene in his Uzumaki bloodline that got activated under certain circumstances, like during a near - death experience or a powerful chakra surge.
In some fanfictions, it could be due to a genetic mutation or an unexpected side - effect of a jutsu he uses. For example, if he experiments with a new form of chakra manipulation, it might accidentally give him the power to summon swords. Or maybe it's a gift from the Sage of Six Paths in a different interpretation of the Naruto universe.