Most commentators believe rightly that the last five verses of chapter 20 belong with chapter 21. The green tree and the dry tree (v47) signifying the same as faces, represent the righteous and the wicked and are most probably alluded to by Christ in Luke 23:31. “If such things befall one who has done nothing to provoke them (even Christ himself), what may be expected for those who are the fit objects of heaven’s vengeance?” (Fairbairn). “If righteous men suffer, how much more the wicked?” (Gill).
Both righteous and wicked would be cut off by the sword of Babylon, some would die and others be taken captive. Gill says,” though they shall not perish everlastingly together, yet may fall together in temporal calamities; the one may be chastised, and the other condemned; or the one be carried captive for their good, as Ezekiel and Daniel and others be cut off by sword and famine; and such as were captives, never the better for their captivity.” The sword is sharp and shining.
“What if the sword contemn even the rod?” (v13), meaning the sceptre: the king of Judah, and his family; (the sword would) “not only come upon and cut off the people and the princes, but the royal family also; and even overturn the tribe of Judah, as the word also signifies; and subvert the government of it, of which the rod or sceptre is an ensign; the rod or sceptre shall be no more in one of David’s line, of the tribe Judah, until the Messiah comes” (Gill).
Nebuchadnezzar, the instrument of God’s anger must first be sent against Jerusalem and then against Ammon. Fairbairn rightly sees the wonderful superintendence of God in this, even using the pagan superstitious divination of the king to accomplish his purposes. Later in the chapter (vv25-27) the king and high priest are addressed as those totally bereft of their status, true priestly dignity and proper regal glory only to be reinstated when the one who has a right to them, namely Messiah, has come. Zechariah is even more explicit a few years later, “even he shall build the temple of the Lord; and he shall bear the glory, and shall sit and rule upon his throne; and he shall be a priest upon his throne: and the counsel of peace shall be between them both.” (Zechariah 6:13). Our Messiah is the only one, of the same order as Melchizedek to combine the high offices of priest and king of God’s people!
There would be some hope for a remnant from Jerusalem but Ammon would be destroyed without remedy.