Ezekiel 21:3 speaks of God drawing His sword against Jerusalem, similar to Jeremiah 21:5 where God declares He will fight against Jerusalem with an outstretched hand and a mighty arm.
Ezekiel 21:6 commands the prophet to groan as a sign of the coming judgment, similar to Ezekiel 24:16-17 where Ezekiel is told not to mourn outwardly for his wife as a sign to the people.
Ezekiel 21:10 describes the sword sharpened for slaughter, paralleling Isaiah 34:5-6 where the sword of the Lord is filled with blood and descends in judgment.
Ezekiel 21:27 speaks of overturning until He comes whose right it is, echoing Genesis 49:10 which prophesies the coming of Shiloh to whom the scepter belongs.
Ezekiel 21:30 calls for the sword to return to its sheath, similar to Isaiah 13:5 where the Lord's weapons of indignation are gathered for destruction.