In episode TWO HUNDRED AND FORTY-ONE, Mike, Wade, and Jason discuss theology by twos (law and gospel, theology of the cross and theology of glory, two kinds of righteousness, two kingdoms, etc.).
Christ has received the mark of law that we might be marked with the gospel, with the sign of his holy cross on our heads and hearts as redeemed children of God.
Ultimately, however, we find in the Heidelberg Disputation the root and core of Luther’s theology, which he would build and expound upon throughout his life.