Why did they have to take the Ark to the mountain in the island to open it?

Question

In Raiders of the lost Ark Belloq and the German army take the Ark on top of a mountain in an island to perform a ritual to open the Ark and look inside

I must have missed something in the movie because I don't understand why they needed to go there to look into the Ark in the first place

I know Belloq would probably insist on going there as it is a part of a ritual for him and he personally would understand the value of opening the Ark there, but the German Commanders wanted to take the Ark to Berlin as soon as possible and were not much interested in anything else, and the only reason they agreed with Belloq was because he made the point that it was better to make sure it was the real Ark before opening it in front of Hitler

This fear was the only reason they would even agree to look into the Ark before going back to Berlin, but they could as well have forced Belloq to open the Ark on the ship (the one the Germans hijacked, the one in which Indy was escaping with the Ark) and make sure it was the real one

What was the reason they had to take the Ark to the mountain to perform the ritual before opening it?

(I believe there was a deleted scene which explains some of the Ark plot points, but this doesn't explain much about having to go to the mountain either. From the deleted scene it is clear how Indy knew not to touch nor look at the Ark, but since this scene was removed from the movie the German Army shouldn't know about not touching the Ark, but throughout the movie they are still careful about not touching the Ark anyway. If Belloq knew about not touching the Ark and this was the reason for having to go to the mountain to perform the ritual, why wouldn't he know that he shouldn't look into the Ark? )

Answer 1

Belloq was evidently quite taken with the "tabernacle" as a potential spot to open the ark. In the film script it's described in considerable detail

INT. THE TABERNACLE
The light in here is lovely, unearthly. Oil lamps burn. The Tabernacle is really several concentric, silk tents, which creates a flowing maze effect. The innermost tent has at its center a 3-foot high, tapestry-covered altar. Belloq watches with gleaming, obsessed eyes as two Nazis carefully lift the actual Ark out of its crate by means of the long poles. The Ark dazzles the eye, seeming to glow gold in this strange light. The two Nazis place it carefully on the altar. Shliemann and some Aides hang back. Marion is nowhere to be seen.

And the film's official novelisation gives us some insight into the site's historic significance as well as Belloq's thought process:

The Frenchman was staring beyond the clearing to a stone outcropping on the other side - a pinnacle some thirty feet high with a flat slab at the top. Into the sides of the slope some ancient tribe, some lost species, had carved primitive steps. The appearance was like an altar - and it was this fact that had brought Belloq here. An altar, a natural arrangement of rock that might have been designed by God for the very purpose of opening the Ark.

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As to why they needed to open it using the traditional Jewish rituals (e.g. as opposed to just taking the lid off), this is also described. The simplest explanation is that the German commander chooses to defer to the resident expert in matters regarding the Ark. Belloq says that they need the ritual, therefore they need the ritual:

“I am going to open the Ark,” Belloq said. “However, there are certain … certain preconditions connected with the act.”
“Preconditions? Such as?”
“I don’t think you should worry, my friend. I don’t want to be the one responsible for overloading your already much-worked brain.”
“You can spare me the sarcasm, Belloq. Sometimes it seems to me that you forget who is in charge here.”
Belloq stared at the crate for a time. “You must understand-it is not simply the act of opening a box, Dietrich. There is a certain amount of ritual involved. We are not exactly dealing with a box of hand grenades, you understand. This is not any ordinary undertaking.”
“What ritual?”
“You will see in good time, Dietrich. However, it need not alarm you.”
“If anything happens to the Ark, Belloq, anything, I will personally pull the hanging rope on your scaffold. Do you understand me?”