Boruto Two Blue Vortex recently stated that Kashin Koji has an ability called Prescience, which allows him to see many different futures. That led to him telling the protagonist that he shouldn't engage Jura in combat because he would lose, but a recent theory suggests that perhaps he lied when he said that since he is worried that Naruto Uzumaki's son could win.
There is an argument to be made in this theory that Boruto could defeat Jura in a one-on-one battle but would require him to reach out to Momoshiki from within. Therefore, this is something that could cause the protagonist to lose his own autonomy, which is perhaps Kashin Koji's concern and could spell doom for the main character if he doesn't adhere to his ally's words.
Disclaimer: This article is a speculative theory and reflects the writer's opinion.
Explaining how Kashin Koji could be protecting Boruto from Momoshiki taking over

It was confirmed in the recent chapters of the manga that Kashin Koji has the ability to see multiple possible futures, which is something that could lead to teasing the upcoming events of the story. In that regard, he told the protagonist to avoid fighting Jura, and the reason could be that the sequence of events could lead Momoshiki to take over his body on a permanent basis.
It has been established for a while in the manga that Momoshiki is living within the body of Naruto Uzumaki's son, and that seems to be a ticking time bomb that is bound to explode at any moment. Therefore, when considering that Jura could push him quite a lot in combat, it makes a lot of sense that this could give the Otsutsuki an opening to take control of his body.
There is no denying that the plot point of the main character's issues with the autonomy of his body is going to pay off at some moment in the series, which is something that could be in this particular situation. Furthermore, it is a point that could explain Kashin's words and also provide greater context for a twist in the story.
The element of different futures in the series

It is very likely that Ikemoto is using the possibility of multiple futures in Boruto as a way to explore different avenues in the series moving forward. Moreover, this is something that could provide fans with expanding the franchise's lore and the multiple directions it could take, even going as far as having a degree of a meta element.
This is also quite interesting when considering the opening scene of the anime, where it features the protagonist facing Kawaki over the remains of a destroyed Konoha, which could be a red herring. It is difficult to address at the moment, but there is no doubt that Kashin Koji's visions might serve a grander vision in the story.
Final thoughts
It is very clear that Boruto's struggles with Momoshiki is a subplot that is going to deliver at some point in the story, and his potential battle with Jura could be that. In that regard, there is an argument to be made that Kashin Koji knows that and is trying to save the protagonist from dooming himself.
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