Commentary for Eruvin 4:7

"That [verse] is written regarding the Ark" - which is the burden of the sons of Kehath, and because it is holier than the other burdens, it is called "Mikdash" (Sanctuary).

"They learn from the doorway of the courtyard gate" - He objects regarding the width, as we learned in the Mishnah, "and the width [must be] less than ten cubits." Now, we find the doorway of the courtyard, which was twenty [cubits] wide, and it is called "doorway," as it is written, "and the curtains of the courtyard, and the screen for the doorway of the courtyard gate," written in the section of Naso. But regarding the height, to disqualify [a doorway] with a height greater than five cubits, he cannot object, for we find the doorway of the Temple, which was twenty [cubits] high, and it calls it "doorway."

The width of the courtyard of the Tabernacle was 50 cubits. Now, as for what is written "fifty by fifty" in the second chapter (Exodus 27:18), it explains it: and its entrance was in the middle of its width, and they closed it with curtains, 15 cubits on this side of the entrance and 15 cubits on that side of the entrance, leaving 20 cubits of width in the middle, as it is written, "fifteen cubits of curtains for the shoulder," and "shoulder" is the side of the entrance.

"Just as below" - [meaning] a height of five [cubits], for all the curtains of the courtyard surrounding [the Tabernacle] were no taller than five [cubits], as it is written (Exodus 27:18), "and its height was five cubits."

"It is regarding its height that it is written" - that the height of the eastern curtains on both sides of the entrance was 15 cubits more than the other curtains of the courtyard, which had a height of 20 [cubits], and no measurement was given for the width.

"From the edge of the curtains and downward" - Below those 15 [cubits] that were added on this side and that side of the entrance, there were another five [cubits] of height, equal to the other curtains, and upon them were added 15 in height on both sides of the entrance, making them 20 [cubits high]. Another interpretation: "It is regarding its height that it is written," that the height of all the curtains of the courtyard surrounding [the Tabernacle] was 15 cubits, but we did not learn a measurement for the width of the entrance. And according to this interpretation, we read in the conclusion, "that [verse] is from the edge of the altar and upward," since the altar's height was ten [cubits], and the curtains were five [cubits] higher than it, making them 15, so that a priest would not be standing on it with the [sacrificial] service in his hand, and all the people seeing him from outside. And I have heard both [interpretations], and this [second one] is the main one, and so it is explicitly stated in Zevachim in the chapter "Kodshei Kodashim" (Zevachim 59a). And the one who explains according to the first interpretation is mistaken, for he assumed that the one who objects, "Let us learn from the doorway of the courtyard gate," objects regarding the height, to disqualify a height greater than five cubits. And for this reason, he turned back to establish the courtyard gate at a height of twenty [cubits].

The Tosafot's Question:

"But now, wouldn't the 'form of a doorway' not benefit him?" - If having a specific type of opening is enough to make the Eruv valid (as implied by the Gemara), then why wouldn't simply shaping the opening like a doorway always work?

The Tosafot's Answer:

"But he doesn't ask, 'Wouldn't doors benefit him?'" - The Gemara doesn't even bother asking the more obvious question: Why aren't doors enough to create a valid Eruv?

"Because it's obvious, since it has doors and they are locked, it's like an upper partition." - Having doors that can be locked is clearly sufficient, as it functions as a wall and effectively encloses the space.

"It's also not relevant to ask, 'Doesn't it require the form of a doorway?'" - There's no need to even bring up the question of whether a doorway shape is necessary.

"Because the form of a doorway is only for aesthetic purposes." - The shape of a doorway is merely decorative; it has no inherent halachic (Jewish legal) significance in creating an enclosed space.

"But this question is well-placed, 'Wouldn't the form of a doorway benefit him?'" - The Tosafot clarifies that the original question about the doorway shape is valid in this specific case.

"Because if it was considered a doorway even when very large, by means of the form of a doorway, he could make it equal to a hall." - Here's the crux of the issue: If any large opening could be considered a valid "doorway" just by shaping it like one, people could make huge openings and still claim it's a valid Eruv, which is not allowed. The Eruv rules have size limits for openings.