Is believing a physical action or a heart attitude?
Believing is an attitude of the heart, not a physical action performed with hands or feet. Scripture distinguishes inward belief from outward verbal confession: one believes in the heart that God raised Jesus from the dead, and one confesses with the mouth the Lord Jesus, resulting in salvation.
Les explains that Romans 10:9 calls for verbal confession with the mouth—calling on Him out loud for salvation—but faith itself is inward. He says believing is not something you do with your hands or your feet; believing is an attitude of the heart. The heart believes that God raised Jesus from the dead, which implies Christ died and rose again, and the promise attached is that you shall be saved.
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.