Verses 18 and 19 are references to Micah 4:12 and 13.
After Israel becomes more powerful, the gathering will occur. These are God’s people. To be gathered as sheaves into the floor represents gathering something of value. The result of the gathering will be a strengthening of the house of Israel, and God will be the King, dispensing justice through his “sword of … justice.”
Verse 21 says that “I will establish my people, O house of Israel.” The house of Israel already exists, so the establishment cannot be a beginning, but perhaps the creation of a firmer foundation of the house of Israel. With the gathered Israel together, God can become the King to rule on earth during the millennium.
After discussing the establishment of the whole of the house of Israel, Jesus turns to the subject of this land and this people. They, too, will be established in the land. Those of the New World house of Israel will be the leadership of the gathered house of Israel for those in the New World. “The powers of heaven shall be in the midst of this people; yea, even I will be in the midst of [them].” When they are established as the New World governing body for the house of Israel, Jesus will be with them. Having the resurrected Savior be the one to say this, the people understand that the same Savior will be in their midst at that future time.