The Old Calendar is not God, nor the Holy Spirit. It is Tradition, which they ought not to have despised; they ought to have respected it. They did not entirely reject it, however, as the Iconoclasts rejected the Icons and burned them. They did not cast the Saints out of the Church, they did not burn the calendar, they did not deny God, the Mysteries, or the Holy Spirit.
The Holy Fathers, who prescribed that the Feast of Pascha be celebrated according to the Julian Calendar, did not tell us: “With that [the Julian Calendar] you will celebrate the Mysteries; with that you will be saved; if you have that you are able to commit all manner of sins, to cast aside love, to have enemies amongst yourselves, to insult one another, to accuse one another, to anathematize one another, to beat one another, even inside Churches—you are free. You can do all of this, just as long as you keep the Old Calendar.”
The Holy Fathers who prescribed the Old Calendar did not become Saints because they kept the Old Calendar. They became Saints because they kept the Orthodox Faith, love, humility, and the other virtues. (Source: http://www.hsir.org/Theology_en/E3a3b004AgNektariosAK323.pdf)