It is thought that the first reference to a fir or pine tree being used as a symbol of Christmas came about around the 700's when St. Boniface cut down the Oak of Thor in Germany. When there was no response from "Thor", Boniface pointed to a fir tree and said that it was the symbol of Christ that people should look to as it was ever green in the midst of winter darkness.
Later, in the middle ages, a Paradise Tree was used in plays on December 24th, which was then known as the feast day of Adam and Eve. The evergreen tree was decorated with apples and later, communion wafers and candles. The communion wafers were a symbol of forgiveness, the candles as symbol of the Light of Christ and the apples a symbol of our sinful nature.
One legend of Christmas is that Martin Luther, the great reformer, brought a fir tree into his home after being inspired on a walk by the the beautiful starry sky and snow covered evergreens. He lit the tree with candles and said that the candles were symbolic of the light of Christ and a reminder of the starry sky above Bethlehem on the first Christmas night.
It wasn't until the 1600's that Christmas trees really started to become popular. In those days, trees were small and placed on a table top. Their use spread from Germany to France and throughout Europe and the U.S. Until the advent of electric lights, candles continued to be used though usually were only lit on Christmas Eve.
Today, people give the Christmas tree many meanings. For some, the evergreen tree represents everlasting life. Some say that the uplifting branches and the upward pointing needles all point up to heaven.
Others call it the "Jesse Tree" as a reference to the lineage of Jesus and how Jesus descended from the line of King David through his father Jesse.
The Christmas Tree can also be used a symbol of Christ's resurrection as the tree is cut down and the erected again.
It also reminds us of the "tree" on which Jesus was crucified as a pure sacrifice for our sins.
He himself bore our sins in his body on the tree, that we might die to sin and live to righteousness. By his wounds you have been healed.
1 Peter 2:24
The ornaments on the tree are emblematic of our fruitful lives as Christians.
I am like an evergreen cypress,
from me comes your fruit.
Blessed is the man who trusts in the Lord,
whose trust is the Lord.
He is like a tree planted by water,
that sends out it's roots by the stream,
and does not fear when heat comes,
for its leaves remain green,
and is not anxious in the year of drought,
for it does not cease to bear fruit."
Jeremiah 17: 7-8