St. Symeon the New Theologian (949-1022) was absolutely insistent that every believer must receive a second baptism, the Baptism of the Holy Spirit. It is not to be confused with ritual Orthodox Chrismation.
“… ‘John Baptized with water, but you shall be baptized with the Holy Spirit’. If one is ignorant of the Baptism wherewith he was baptized as a child and does not even realize that he was baptized, but only accepts it by faith and then wipes it away with thousands upon thousands of sins, and if he denies the second Baptism – I mean, that which is through the Spirit, given from above by the loving-kindness of God to those who seek it by penitence – by what other means can he ever obtain salvation? By no means!” ~ The Discourses. XXXII