zechariah 4:7 Who art thou, O great mountain? before Zerubbabel thou shalt become a plain: and he shall bring forth the headstone thereof with shoutings, crying, Grace, grace unto it. - Free Bible Online

      7. All mountain-like obstacles (Isa 40:4; 49:11) in Zerubbabel's way shall be removed, so that the crowning top-stone shall be put on, and the completion of the work be acknowledged as wholly of "grace." Antitypically, the antichristian last foe of Israel, the obstacle preventing her establishment in Palestine, about to be crushed before Messiah, is probably meant (Jer 51:25; Da 2:34, 44; Mt 21:44).
      bring forth the head-stone--Primarily, bring it forth from the place where it was chiselled and give it to the workmen to put on the top of the building. It was customary for chief magistrates to lay the foundation, and also the crowning top-stone (compare Ezr 3:10). Antitypically, the reference is to the time when the full number of the spiritual Church shall be completed, and also when "all Israel shall be saved" (compare Ro 11:26; Heb 11:40; 12:22, 23; Re 7:4-9).
      Grace, grace--The repetition expresses, Grace from first to last (Isa 26:3, Margin). Thus the Jews are urged to pray perseveringly and earnestly that the same grace which completed it may always preserve it. "Shoutings" of acclamation accompanied the foundation of the literal temple (Ezr 3:11, 13). So shoutings of "Hosanna" greeted the Saviour in entering Jerusalem (Mt 21:9), when about to complete the purchase of salvation by His death: His Body being the second temple, or place of God's inhabitation (Joh 2:20, 21). So when the full number of the saints and of Israel is complete, and God shall say, "It is done," then again shall "a great voice of much people in heaven" attribute all to the "grace" of God, saying, "Alleluia! Salvation, and glory, and honor, and power, unto the Lord our God" (Re 19:1, 6). Ps 118:22 regards Him as "the head-stone of the corner," that is, the foundation-stone. Compare the angels acclamations at His birth, Lu 2:14. Here it is the top-stone. Messiah is not only the "Author," but also the Finisher (Heb 12:2). "Grace" is ascribed "unto it," that is, the stone, Messiah. Hence the benediction begins, "The grace of the Lord Jesus Christ" (2Co 13:14).

JFB.