Try to look past our supercessionist interpretation of the phrase "new covenant" all the way back to how Jeremiah's listeners would have understood it. "This covenant will be written on your hearts."
John H. Hayes In Preaching through the Christian Year B:
The newness is a special gift, the capacity to be faithful and obedient. In the Old Testament, the heart is the seat of the will (see Jeremiah 29:13; 32:39; Ezekiel 1:19; 36:26); consequently, the special gift here is a will with the capacity to be faithful. God thus promises to change the people from the inside out, to give them a center. This covenant will overcome the conflict between knowing or wanting one thing and doing another...The Lord is promising not new content but new contact--or, renewed contact.
Lectio Divina: Jeremiah 31:33-34