St. Maximus the Confessor ca. 580-662
Our salvation does not depend merely on faith of the heart. The Lord teaches, Whosoever shall deny Me before men, him will I also deny before My Father Which is in heaven. Furthermore, the divine Apostle tells us, With the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. If God and the Prophets and Apostles command that the mystery of faith which is the salvation of the whole world be confessed openly, then our salvation is hindered when its proclamation is forbidden. (St. Dimitri Rostov: Life of St. Maximus)
