Why does the Pasuk emphasize the fact that four kings were fighting against five?
Rashi: Bearing in mind that the four kings were victorious, it is coming to tell us that, despite the four kings' might,
Avraham did not hesitate to chase after them.
Gur Aryeh: How do we see this from this verse in particular? We might have thought that the four happened to win by chance. The Pasuk emphasizes "the four kings against the five" (which we already know), to show that this was unusual, and due to their great might.