20. it--the altar and pillar.
      a sign--(of the fulfilment of prophecy) to their contemporaries.
      a witness--to their descendants.
      unto the Lord--no longer, to their idols, but to Jehovah.
      for they shall cry--or, "a sign . . . that they cried, . . . and He sent to them a saviour"; probably, Alexander the Great (so "a great one"), whom the Egyptians welcomed as a deliverer (Greek, Soter, a title of the Ptolemies) out of the hands of the Persians, who under Cambyses had been their "oppressors." At Alexandria, called from him, the Old Testament was translated into Greek for the Greek-speaking Jews, who in large numbers dwelt in Egypt under the Ptolemies, his successors. Messiah is the antitype ultimately intended (compare Ac 2:10, "Egypt").

JFB.