1)
Why does it repeat that there were 600 men with Sha'ul?
1.
Radak: This teaches that no others joined with him. Even though [Yisraelim] should [have joined with him to] fight the Pelishtim [and they did not], Hashem saved them.
2.
Malbim: This explains why he was on the opposite side from the Pelishtim. Because he had so few men, he did not want that they will see each other.
