You're more likely to see a beard in the pulpit today than at any time since the 1800s. But beards—especially among clergy—were once serious, symbolic matters. They separated East from West during the Great Schism, priests from laity during the Middle Ages, and Protestants from Catholics during the Reformation. Some church leaders required them; others banned them. To medieval theologians, they represented both holiness and sin. But historian Giles Constable says that rules on beards sound more forceful than they really were. Clergy (especially powerful ones) were likely to follow fashion in their day, too.
Clement of Alexandria calls the beard "the mark of a man" and says "it is therefore unholy to desecrate the symbol of manhood." Many other church fathers made similar remarks about beardly manliness. But most early church clergy were either beardless or had a closely trimmed beard.
Roman Emperor Julian sports a beard to show his break with the shaven Christian emperors before him, and to mark his connection to pagan Roman religion.
Euthymius says only men with a beard can enter his Judean Desert monastery, not boys "with female faces."
A rule is made that "no cleric should grow long hair or shave his beard." It's very out of step with its time, and several copyists simply changed it to "No cleric should grow long hair or [a long] beard." It seems to have been ignored in its day but became widely referenced in the 1100s and 1200s.
The Council of Aachen requires monks to shave every 15 days (24 times a year). Other monastic communities adopt similar rules, though some only require a shave six or seven times ...