What is important is the worship and joy associated with His birth and the thankfulness for what Christ has done for mankind. The day doesn't matter. Focus on WHY Christmas is celebrated, rather than on the date which is in essence form over substance.
God says the day does matter.
The word of God gives us a celebration for his son’s birth, the day he came to Tabernacle with us. It was the 15th day of the Biblical month Tishri, which places his birth in September by our calendar.
YHVH doesn’t tell us things that don’t matter. If we ignore the rehearsals that YHVH prescribed, we will not be ready when it isn’t a rehearsal any more. Sukkot is when he will return, but which Sukkot? This is what the parable of the virgins is all about; those that ignore Sukkot, and pretend that he was born on Tammuz’s birthday are the foolish virgins. Do you wish to be one of them?