It isnt so often that there was something special about respecting the Christmas or Winter season to not fight, but that it was incredibly impractical to.

Pre-modern forces would almost always stop campaigning, go into winder quarters, and await better weather come Spring when hey could march again. Snow, the cold, mud, lack of forage, all sorts of issues made it hard to move an army by foot and horse and to fight in Winter. And really even the thaw didnt mean the fighting was easy again, more mud, swollen rivers, and such would push the start of campaigning back months.

Washington was campaigning in December not cause he wanted to but because he had to, having been pushed across New Jersey the previous weeks, and as soon as he could secure some sort of stand he too would go into quarters. After Trenton and a few days later Princeton he marched to Morristown, NJ and went into Winter Quarters, the first of several Winters the Contientals would spend there. The next year after fighting south of Philly in an attempt to prevent a British attack, Washington went into quarters famously at Valley Forge, where the army spent a good deal of time complaining about the food, tending its wounds, and attempting to reinvent itself as a better trained and prepared force.

So yes it was the normal practice, even for Washington, to see a lul in the fighting in winter as it was simply too difficult not to.