26. This verse stands instead of the sentence which we should expect, to correspond to Ga 4:24, "One from Mount Sinai," namely, the other covenant from the heavenly mount above, which is (answers in the allegory to) Sarah.
      Jerusalem . . . above-- (Heb 12:22), "the heavenly Jerusalem." "New Jerusalem, which cometh down out of heaven from my God" (Re 3:12; 21:2). Here "the Messianic theocracy, which before Christ's second appearing is the Church, and after it, Christ's kingdom of glory" [MEYER].
      free--as Sarah was; opposed to "she is in bondage" (Ga 4:25).
      all--omitted in many of the oldest manuscripts, though supported by some. "Mother of us," namely, believers who are already members of the invisible Church, the heavenly Jerusalem, hereafter to be manifested (Heb 12:22).

JFB.