Romans 10:9–10 is arranged in a straightforward chiasm:
A. If you confess with your mouth Jesus as Lord
B. and believe in your heart that God raised Him from the dead,
C. You shall be saved.
B’. For with the heart man believes unto righteousness
A’. and with the mouth he confesses unto salvation.
Paul moves from mouth to heart, then from heart to mouth. He moves from confession to belief, and then from belief to confession. It’s significant that Paul doesn’t invert the order; it’s not heart-mouth-mouth-heart, with the heart on the “outside” of the structure. The textual arrangement mimics the meaning: “Heart” is interior to “mouth,” and mouth is the outside expression of the heart.
Salvation is in the heart of the heart of the text. The first half (A–C) might be taken to imply that salvation is more closely associated with belief in the heart than it is with confession with the mouth. But the second half complicates that. Structurally, the two uses of “salvation” words (sozo and soteria) knot up the chiasm, linking A’ to C instead of to A.
Substantively, the double use of the root indicates that salvation doesn’t come from heart belief alone. Salvation results from the work of two organs, the heart and the mouth. Heart-belief is absolutely necessary, but not sufficient to achieve salvation. The interior heart has to emerge into the public forum, verbalized in confession.