The thickness of the wall, which was for the side chamber on the outside, was five cubits: and that which was left was the place of the side chambers that were inside.
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George Leo Haydock
House. Because these side-chambers were in the very walls of the temple all around: or it may also be rendered, (more agreeably to the Hebrew) so as to signify, that the thickness of the wall for the side-chambers within was the same as that of the wall without; that is, equally five cubits. (Challoner)
Protestants, "and that which was left, was the place of the side-chambers that were within. "(Haydock)
To manifest a greater respect for God, the apartments of the priests were twenty-five cubits distant from the temple, (ver. 10.) and divided by a wall, which Josephus describes as three cubits high. (Antiquities viii. 2.) This wall was at the distance of five cubits from the temple. (Calmet)