At some point during this Advent season and the coming of Christmas, you will log on to your computer, and you will see somebody smugly opining that ‘actually Christmas is a pagan festival’.

This person will not know anything about pagans, bar some fuzzy ideas about equinoxes (always with the equinoxes) and sacrifice. The reasons given for this will vary: we put up trees in our houses and decorate them, just like pagans! We light candles! And we give presents, like the Romans did at Saturnalia or the Vikings at Yule or [insert random pagan festival here]. And 25 December is actually the festival of the Roman god Sol Invictus! And it’s near the solstice! And doesn’t it all have something to do with Mithras anyway? By this point, I will have slowly torn out enough of my hair to craft a Christmas stocking.

What’s worse is that these canards are usually posted by people of intelligence and some historical acuity. But somehow, when it comes to Christianity, there remains a deep-seated desire to say that it’s all rubbish. All of this matters, though – whether you are a Christian or not.

Let’s start with the date. Early Christians – and remember that Britain had been Christian since the Romans, and that the invading Anglo-Saxons and Vikings converted pretty damn quickly – weren’t that bothered about the birth of Jesus. When they started getting interested, various dates were posited, and eventually, influenced by a tradition that........

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