From 1951 to 1957 he belonged to the [[clergy]] of the Vologda [[diocese]]. On [[February 27]], 1957, he was arrested by the KGB and charged for "anti-Soviet agitation" (due to his possession of religious books and conversations with believers). On [[May 16]], 1957, he was sentenced to 10 years imprisonment. He served his sentence in the political camps of Mordovia (Dubravlag). On [[September 12]], 1960, the Supreme Court of Mordovia reduced the sentence to five years, and then by the court's resolution he was released from custody ahead of time and put on probation. (He was rehabilitated on [[October 14]], 1988). In November 1960 he came back to Estonia and became rector of John the Forerunner Church in Tallinn.
On [[July 20]], 1990 at the first meeting of the [[Holy Synod]], chaired by His Holiness Patriarch [[Alexei II (Ridiger) of Moscow|Alexei II of Moscow and all Russia]], he was appointed [[Bishop]] of Tallinn, vicar to His Holiness the Patriarch. On [[August 21]], 1990, he took [[monasticism|monastic]] vows in the Monastery of the Dormition at Pechery near Pskov and obtained the name of Cornelius; on [[September 6]], 1990 he was elevated to the rank of [[archimandrite]].
On [[September 15]], 1990, he was ordained a bishop at the Cathedral of St. [[Alexander Nevsky]] in Tallinn. The chirotony (laying on of hands) was done by His Holiness Alexei II, Patriarch of Moscow and all Russia; Metropolitan Tikhon of Helsinki (Finnish Orthodox Church), Bishop Evgeny of Tambov and Michurinsk, Bishop Victor of Podolsk, and Bishop Lev of Novgorod and Staraya Russa. Upon the decision of the Holy Synod to grant autonomy to the Estonian Orthodox Church, he became the head of the Estonian church, with the title of Bishop of Tallinn and all Estonia. In 1995 he was elevated to the rank of [[archbishop]].