During the first two centuries after the death of Jesus, Christmas was not celebrated. In 245, when a group of scholars attempted to determine the exact date of his birth, a church council denounced the endeavor, declaring it would be wrong to celebrate the birthday "as though he were a King Pharaoh."
Still, attempts were made to pinpoint Jesus' birthday. The result was multiple dates: January 1, January 6, March 25, and May 20. Initially, the May date was favored because the Gospel of Luke (Luke 2:8) reports that the shepherds who received the announcement of the birth were watching their sheep by night. Shepherds guarded their flocks day and night only during lambing time, which was in the spring. In winter, the animals were generally enclosed in corrals, unwatched.
In 349 Pope Julius formally selected December 25 as the day for Christmas. This date was already widely celebrated in the Roman world as citizens observed the Natalis Solis Invicti (the Birthday of the Inconquerable Sun) in honor of the sun god, Mithras. The festival took place just after the winter solstice, when the days become longer.
Many modern Christmas customs such as decorating a house with greenery, exchanging gifts, and enjoying festive meals originated with this pagan celebration. Scholars believe that Pope Julius selected December 25 as the date of the Nativity to win over followers of Mithras as well as to give Christians an opportunity to honor Christ's birth.
In seventeenth century England, the Puritans objected to Christian celebrations that had no clear biblical basis (the Bible does not tell us to celebrate Jesus' birthday). As a result, the English Parliament in 1643 outlawed Christmas, Easter, and other Christian holidays. However, December 25 as a festive day was so popular that by 1660 the citizens reclaimed it.
When the Pilgrims arrived in Plymouth, Massachusetts in 1620 they also brought with them a distrust of Christmas. A 1659 Massachusetts law fined people for celebrating on December 25. But again, the day was so popular thatthe law was repealed in 1681, although strong religious opposition lasted into the next century.
Christmas is the only religious holiday in America that is also a national legal holiday. In 1836, Alabama became the first state to declare Christmas an official holiday. Oklahoma was the last, in 1907. (adapted from info posted by Victor M. Parachin)