“And say to them, Thus says the Lord Yahweh, Behold I will take the children of Israel from among the nations where they have gone, and will gather them on every side, and bring them to their own land, and I will make them one nation in the land, on the mountains of Israel, and one king will be king to them all, and they will no more be two nations, nor will they be divided into two kingdoms any more at all.”
The world had been divided at Babel (Babylon - Genesis 11:1-9). Then later God's covenant people had been divided. Now the process of healing and restoration was to begin by their being restored to their land and cemented together as one nation in the land. Then they would come under one king, a son of David ruling over formerly divided Israel. Note the rare use of the word ‘king' by Ezekiel in relation to the rulers of Israel. Elsewhere it is only used where captivity was in mind or where they are demeaned (Ezekiel 1:2; Ezekiel 7:27; Ezekiel 17:12-16; Ezekiel 43:7). For it was Yahweh and His chosen future representative who were truly king over Israel.
The fact that they were to be ‘gathered in from every side' again confirms that Israelites were expected to return from many lands. And the purpose of this was that they may be made as one under one king. And when Jesus, the son of David, came, proclaiming the Kingly Rule of God this was His aim, ‘that they may be one even as we are' (John 17:22).