The Roman Catholic Church has traditionally celebrated St. Anastasius on the following day, April 21, though this memorial is not widely celebrated in modern times. The Eastern Orthodox churches, meanwhile, commemorate him on the same date as their Eastern Catholic counterparts.
Even within the Eastern Christian tradition, St. Anastasius' legacy has been somewhat obscured by the renown of other authors. In his own era, however, the Sianite's writings were acclaimed as the work of a “new Moses.” At least one of his works, the “Hodegos” (or “Guide”), remained in use within the Greek Church for many centuries.
No extensive biography of Anastasius exists, and it is unclear whether he was born in Egypt (as some traditional accounts relate) or in Cyprus. His date of birth is also unknown.
In his own writings, Anastasius speaks of being captivated by the proclamation of the Gospel during church services, and being awestruck by Christ's Eucharistic presence as a young man. He eventually made a pilgrimage to Jerusalem, and took up residence as a monk on Mount Sinai in Egypt around the middle of the seventh century. He eventually became the abbot of St. Catherine's Monastery.
Anastasius' life was outwardly uneventful in most respects, though he did leave his monastic cell to defend the Church's teachings against heresy and error. He met or learned about many holy men in the course of his travels, and described their lives in writings that survive to this day.
Among Anastasius' doctrinal opponents were the monophysites, who were in error regarding Jesus' divine and human natures; and the monothelites, who professed a related error regarding Christ's human and divine wills. Though he was not the most important opponent of either heresy, Anastasius' contributions earned him a place among the Church Fathers in the Eastern tradition.
The monk of Sinai also defended the Christian faith against Jewish objections. In one of his major works, the “Commentary on the Six Days of Creation” (or “Hexaemeron”), he explained how the first three chapters of Genesis predicted and prefigured the coming of Jesus Christ. Other surviving writings by the saint include his homilies, and a series of “Questions and Answers” addressing pastoral matters.
St. Anastasius is said to have lived to an old age, and attained to great holiness through prayer and asceticism, by the time of his death sometime after the year 700.
Some confusion has resulted from the conjunction of his Eastern feast day, April 20, with that of another saint who was also named Anastasius and associated with Mount Sinai. But this other St. Anastasius, though celebrated on the same date, lived earlier and led the Church of Antioch.