Christmas Day-December 25-which celebrates the birth of Jesus Christ， the founder of the Christian religion， is the biggest and best-loved holiday in the United States.
According to the Bible， the holy book of Christians， God decided to allow his only son， Jesus Christ， to be born to a human mother and live on earth so that people could understand God better and learn to love God and each other more. "Christmas"- meaning "celebration of Christ "- honors the time when Jesus was born to a young Jewish woman Mary.
Mary was engaged to be married to Joseph， a carpenter， but before they came together， she was found to be with child. Because Joseph， her husband， was a righteous man and did not want to expose her to public disgrace， he had in mind to divorce her quietly. But after he had considered this， an angel of the Lord appeared to him in a dream and said， "Do not be afraid to take Mary home as your wife， because what is conceived in her is from the Holy Spirit. She will give birth to a son， and you are to give him the name Jesus， because he will save his people from their sins."
Although the exact date of the birth of Jesus nearly 2，000 years ago is not known， the calendar on the supposed date divides all time into . (Before Christ )and . ( a Latin phrase， Anno Domini， "in the year of our Lord.")For the first 300 years， Jesus’ birthday was celebrated on different dates. Finally， in the year 354， church leaders chose December 25 as his birthday.
圣诞节只是基督徒庆祝其信仰的耶稣基督(jīdū)诞生的庆祝日。圣诞节的庆祝与基督教同时产生，被推测始于西元1世纪。很长时间以来圣诞节的日期都是没有确定的，因为耶稣确切的出生日期是存在争议的，除了《新约》以外，没有任何记载提到过耶稣;《新约》不知道日期，当然就没有人知道确切日期了。在西元后的头三百年间，耶稣的生日是在不同的日子庆祝的。西元3世纪以前的作家们想把圣诞日定在春分日上下。直到西元3世纪中期，基督教在罗马合法化以后，西元354年罗马主教指定儒略历12月25日为耶稣诞生日。现在的圣诞节日期跟西元纪年的创制是密不可分的。
西元纪年创制于西元5世纪，后来圣诞节这一天就按格里高利历法，即西元纪年的“公历”来确定了，而日历按着假定日期把时间分为公元前(耶稣基督诞生前)和公元后(A. D. 是拉丁文缩写，意思是“有了我们主--耶稣的年代”)。后来，虽然普遍教会都接受12月25日为圣诞节，但又因各地教会使用的历书不同，具体日期不能统一，
