1)
What is the meaning of "Al ha'Shal"?
1.
Rashi (based on Sotah 35a): It is for his Shegagah. He should have made a Kal v'Chomer - the Aron carried across the Yarden those who carried it (refer to Yehoshua 4:11:1:1) - all the more so it can carry itself!
2.
Radak: It is for his Shegagah. Only Leviyim, who are more Mekudash, may carry the Aron! Above (1:7:1) it says that his brother Elazar was Mekadesh him to guard the Aron, i.e. the house in which the Aron was, but he would not stretch out his hand to move it!
2)
Why does it say "Im Aron ha'Elokim"?
1.
Malbim: It is a great sin to forget fear of the King when standing in front of Him!
