So the LORD said to him, “Bring me a heifer, a goat and a ram, each three years old, along with a dove and a young pigeon.” Abram brought all these to him, cut them in two and arranged the halves opposite each other; the birds, however, he did not cut in half...
When the sun had set and darkness had fallen, a smoking firepot with a blazing torch appeared and passed between the pieces. Genesis 15: 9, 10, 17

The men who have violated my covenant and have not fulfilled the terms of the covenant they made before me, I will treat like the calf they cut in two and then walked between its pieces. The leaders of Judah and Jerusalem, the court officials, the priests and all the people of the land who walked between the pieces of the calf, I will hand over to their enemies who seek their lives. Their dead bodies will become food for the birds of the air and the beasts of the earth.  Jeremiah 34:18-20

God told Abraham to cut a sacrifice in half, then, a smoking firepot/blazing torch (God) passed between the pieces.  This represented the agreement to a covenant.

The visual image was saying:

• I will agree to this covenant to my death
• May I be killed and split in two if I ever break my promise
• I sign my name to this covenant in blood and sacrifice

In Jeremiah, the leaders did not follow the terms of the covenant and God reminded them that they promised to the terms of the covenant to their death.  By nullifying the agreement, God would collect their own lives.