1)
Why was Hashem angry at Uza?
1.
Radak: He was not a Levi. David erred; only Leviyim carry the Aron, and not via a wagon. "veli'Vnei Kehas Lo Nasan? ba'Kasef Yisa'u" (Bamidbar 7:9). David confessed his sin, and said "one does not carry Aron ha'Elokim, only via Leviyim", "we did not expound it properly" (15:12-13).
2)
Why does it say that he died "Lifnei ha'Elokim"?
1.
'Rashi': It was Lifnei Aron ha'Elokim. In Shmuel II, 6:7 it says "Im Aron ha'Elokim."
