By St. Nikodemos the Hagiorite
The famed Dositheos, on p. 80 of his Dodekavivlos, writes how although during the time of Pope Urban VIII (1568-1644) it was requested that the memory of Constantine the Great should be celebrated as a Saint, immediately he said yes. Accordingly, in the area of Calabria in Italy, there appears to be an old church of the Saint. Yet, Constantine the Great always was a Saint and Equal to the Apostles, for so he was called in the Minutes of the Ecumenical Synods, as well as in the common and traditional glory of the Church.
Besides, he was anointed Priest and King, through the ministry of his rule, and through the noetic chrism and myrrh of the Priesthood. Thus the Church chants in his doxastikon the following verse: "Receiving the knowledge of the Spirit, you were anointed with oil as Priest and King, supporting the Orthodoxy of the Church of God." Therefore it is written in the Apocalypse: "And have made us kings and priests to our God; and we shall reign on the earth" (Rev. 5:10). Assuredly not everyone who has been baptized in Him is a Priest, as in the nonsense of the Lutherans and Calvinists, but the Orthodox kings are guardians of ecclesiastical affairs and take care of it.
The most Christian Constantine was preeminently a King and Bishop, and one can see in Dositheos, on p. 212 of his Dodekavivlos, where it is proved that Constantine the Great, although an Orthodox king, was a Bishop in twenty-six ways. On the occasion of his entertaining a company of Bishops, the blessed one kindly said to them: "I also am a Bishop. You are Bishops of the inner man, established on the foundation of the Apostles and Prophets. I am a Bishop of the outer and inner man. Of the outer because I take care of their education and correct way of life. It is not without purpose that I wear a sword. Of the inner, because I am a co-worker with you of the certification and increase of the Orthodox faith, also established on the same foundation of the Apostles and Prophets" (P. 217 of the Dodekavivlos).
Dositheos says at this point that Constantine the Great established a law, not to condemn hereafter anyone to death by crucifixion, so that the instrument of salvation and life should not become once again an instrument of condemnation and death. Thus all kings who call themselves Christians, have kept and keep this law, and do not condemn anyone to death by crucifixion.
From The Synaxaristes of the Twelve Months of the Year - May 21. Translated by John Sanidopoulos.