1)
Why was the Aron captured?
2)
Why does it say "Aron Elokim", and not "Aron Bris
1.
Kli Yakar (Lani'ado) #1: Yisrael did not honor the Bris. This is why it was taken.
2.
Kli Yakar (Lani'ado) #2: The Aron was taken for a long time. The Luchos were taken, but promptly returned to Yisrael. Refer to 4:12:1:1. 1
1
Also in verse 6, it says "Aron Hashem", without the word Bris! The Pelishtim said so; perhaps they did not know what was inside. (PF)