why do some Christians wear a mezuzah ?

Wearing a mezuzah? Heh- all it actually does is show how little they know! A mezuzah is commanded to go on the DOORPOSTS! Wearing one as a necklace just shows complete ignorance of the Torah and the fact that they know absolutely nothing about what the Torah actually commands and says. Anyone silly enough to do this needs to do some serious studying

I have one at my front door, but they are also available as a pendent on a necklace. They contain a blessing from Deuteronomy 6:4-9 & 11:13-21.

It begins, "Hear, O Israel, the Lord our God, the Lord is one..."

Most Christians would wear a cross, a crucifix or a religious medal, but, given our heritage from Judaism, a mezuzah could be worn.

Christianity came from Judaism.

Best wishes.

I wore a kippa while at the western wall in Jerusalem, we should remember the passover too, but tradition gives us easter

Smart of you not wanting to be offensive. The answer would be offensive. It is an odd sect of Christians who are offensive. WARNING: OFFENSIVE SITE https://en.wikipedia.org/wiki/Jews_for_Jesus