1)
What is the meaning of "va'Yiten la'Shevi Uzo"?
1.
Rashi: He handed over the Aron and Luchos to the Pelishtim.
2.
Radak: "Uzo v'Sif'arto" is the Aron - "Atah va'Aron Uzecha" (132:8), for via it was seen Hashem's strength and glory. Malbim - the Aron is Uzo due to the Torah in it, and it is Sif'arto, for wonders were done via it.
2)
Why does it say "v'Sif'arto b'Yad Tzar"?
1.
Radak: Pelishtim captured the Aron.
2.
Malbim: The enemy succeeded and glorified themselves.