| Gill's Exposition of the Entire Bible He measured also the porch of the gate within, one reed. This was either the measure of the breadth of the porch between the opposite chambers on both sides; or rather of the length of that space, which was between the third little chamber and the last gate; and such a space must be supposed to be between the first gate and the first little chamber, which space were three yards and a half; which shows how spacious the churches of Christ will be, and how exactly measured.
Geneva Study BibleHe measured also the porch of the gate within, one reed.
Wesley's Notes 40:8 The porch - The posts which were joined together at the top by an arch, and so made the portico.
Matthew Henry's Concise Commentary40:1-49 The Vision of the Temple. - Here is a vision, beginning at ch. 40, and continued to the end of the book, ch. 48, which is justly looked upon to be one of the most difficult portions in all the book of God. When we despair to be satisfied as to any difficulty we meet with, let us bless God that our salvation does not depend upon it, but that things necessary are plain enough; and let us wait till God shall reveal even this unto us. This chapter describes two outward courts of the temple. Whether the personage here mentioned was the Son of God, or a created angel, is not clear. But Christ is both our Altar and our Sacrifice, to whom we must look with faith in all approaches to God; and he is Salvation in the midst of the earth, Ps 74:12, to be looked unto from all quarters. | 
