1)
Why does it say that his house was blessed "Ba'avur Aron ha'Elokim"?
1.
Malbim: Biglal refers to a prior reason. Ba'avur refers to the latter (current) reason. It should have said Biglal, like "va'Yvaracheni Hashem Biglalecha" (Bereishis 30:27). Therefore, Chachamim expounded that it was not due to the Aron; if so, only he should have been blessed, for only he served it! Rather, it was for the Aron, to dispel the notion that it kills in anger. Rather, good and Chesed pursue all close to it. David should learn from this to take it to Ir David.
2)
Why does it say that he took the Aron b'Simchah?
1.
Malbim: It was not with fear, for he saw that Chesed is overpowering.
