The smoking oven and the burning torch symbolize God passing between the pieces. The most important thing to realize is that God walks through alone. Normally, both parties of the covenant would walk through together, showing that they both had responsibilities to keep in order to maintain the covenant. But when God walks through alone, He shows Abram that there is absolutely nothing Abram or his descendants have to do in order for God to keep this covenant.
It is a one sided covenant. God takes all the responsibility for fulfilling it upon Himself. No matter what Abram does or doesn’t do from this point on, God will keep His promise. No matter what Israel has or has not done in history, God will keep His promise. (