Q:

How did Indy know to not look at the Ark?

My grasp of Scripture is poor, but the only thing I can recall in the Bible along these lines is Uzzah being struck down because he TOUCHED the Ark. How did Indy know that they should close their eyes and escape being fried by the Ark?

A:

Cross-referenced from that initial link is 1 Samuel 6:19.

But God struck down some of the men of Beth Shemesh, putting seventy of them to death because they had looked into the ark of the LORD. ..

See also 1 Samuel 6:19 in the King James Bible.

And he smote the men of Bethshemesh, because they had looked into the ark of the LORD, even he smote of the people fifty thousand and threescore and ten men: and the people lamented, because the LORD had smitten many of the people with a great slaughter. 

Those versions are pretty much in agreement, though the number jumped from 70 to over 50 thousand.

A:

It wasn't so much the Ark he wasn't looking at, but the everything.  The Ark, the angels, and the whole thing.
I remember seeing a special on TV, a "Making of" type show, and they had a shot of Spielberg working with Harrison Ford and Karen Allen and he said something to the effect of, "And, according to the Gospel of Lucas, Indy and Marion are spared because of their goodness."  I thought that was interesting because his comment, as the director, indicated that in his mind it wasn't so much whether they looked at the Ark and angels (were they ark-angels?), but that the angels actually distinguished between good people and bad people.

A:

This is a common idea in Judaism. To paraphrase: 
It is impossible for a human to behold God, because He is too mind-boggling for a mortal to comprehend. If you see God, you die. 
This is what my Hebrew instructor taught me.

