Scripture doesn't instruct us to observe the Feast of the Nativity (Christmas). We, that is Christians, do that because we love our Lord Jesus Christ. And the liturgical date is December 25th, following the ancient practice of the Church.
I certainly don't see any biblical teaching that forbids us from honoring the Lord's birth.
But since we're talking things not expressly commanded in Scripture as though they are in and of themselves a problem, perhaps we could start with the Bible itself. I've yet to actually see anywhere in Scripture that teaches
A) A definitive biblical canon and where that canon is itself defined
B) That we are restricted only to the use of Scripture as defined by such a canon.
Now here's the thing. I'm a Lutheran, we're the Sola Scriptura folks. And yet we've never had a problem with the traditions of the ancient Christian Church save for when they conflict with Scripture--that's actually what Sola Scriptura refers to. You see Sola Scriptura does not refer to some sort of "Bible Onlyism", instead it refers to Scripture alone being the infallible Regula Fidei and Norma Normans; that is, the infailing rule of faith and norming norm of Christianity. It means Scripture is the final court of appeal, and we say that in order to regulate doctrine and practice in order that we do not deviate from "the faith once and for all delivered to the saints" in order that we remain faithful and true to the Church's historic and ancient confession, its orthodoxy, and its catholicity.
It isn't a sledgehammer to go ahead smashing at the pillars and foundations of the household of faith and rebuild it from the ground up with the opinions and traditions of men--as has been the practice of most of Protestantism.
-CryptoLutheran