Candles are lit and placed in windows during Christmas as it is the holiday or feast of light. The candles symbolize the pending birth of Jesus Christ.
The tradition of placing candles in windows began in the country of Ireland. The Irish placed candles in the windows as a result of British persecution against the Catholic church. During this time, people were not allowed to attend church and often held secret prayer services in their homes with candles.
In many religions, Jesus is represented by a candle, which has been the practice since medieval times. In some countries, candles are not only placed in the windows, but throughout the home.