If one observes that day unto the Lord, then to the Lord he observes it.
I hear the arguments that there are pagan practices associated with December 25th... but if a saint of God is using that day as a day unto the Lord, not to pagans, then to them it is
not a pagan holiday.
The scriptural principle to be applied here is fairly straightforward:
Romans 14:5 One man esteemeth one day above another: another esteemeth every day alike.
Let every man be fully persuaded in his own mind.
14:6
He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it...
see also ...
Col 2:16 Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:
2:17 Which are a shadow of things to come; but the body is of Christ.