How do we know that heart faith is necessary for salvation?

Romans 10:10 states, 'For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.' This indicates that true faith is deeply rooted in the heart rather than merely in the intellect. It's a work of God that involves trusting Him fully for our salvation. This heart faith acknowledges our dire condition: that we are sinners in need of God's mercy. Thus, it is not sufficient to merely know facts about Jesus; we must personally trust Him from our innermost being, desiring and relying on Him for salvation.