1)
Why did Sha'ul not pursue the Pelishtim?
1.
Radak #1: It is because Hashem did not answer him via the Urim v'Tumim. He thought that even there was reason to exempt Yonason, there is sin among us due to the Shevu'ah.
2.
Radak #2: Since the night passed [amidst the lottery and debating whether to kill Yonason], Pelishtim already went to their place.
