Right I hope no one objects but I have tried to break down the massive Religious Structure: Christian category (107!) into some slightly more manageable chunks.
I don't necessarily want people to pile in on it as the focus was on natural sites, I just had a bit of time to do it so dove in.

This tiny batch (5) is those where the main focus is on pilgrimage routes/ monuments

Bethlehem
Luther Memorials
Baptism Site "Bethany Beyond the Jordan"
Kalwaria Zebrzydowska
Routes of Santiago de Compostela (Spain)
Routes of Santiago de Compostela in France

Why is the French section here and the Spanish one elsewhere?

Well picked up. It is a key word that lumped it in with the cathedrals on my search, will move it now.

My selection would only include the Santiago route in Spain.

Agreed - it picks up the main value of the site . The french one seems an exercise in getting as many villages in France as possible a whs! Some of its highlights in France can be in in their own right or as part of a town/ city.

Similarly we won't need S de Compostela as a separate whs!

Agreed too.

My selection:
Route of Santiago de Compostela (Spain)

Sorry - I was commenting solely on the Santiago pair.
As for the rest, surely Bethlehem has to be included for its religious significance?
Really the List needs to encompass "Protestantism" but I agree that the Luther memorials are just too weak.

I'm going to include the entire Religious Structure: Christian category link for those who need it.

If we're talking Christian pilgrimages, there's really only one site on this list that stands out to me:

1. Routes of Santiago de Compostela (Spain) -- this is a great example of a Catholic pilgrimage route that has been in use since the Middle Ages

That said, I would place two sites listed in other categories above the Routes of Santiago de Compostela for Christian pilgrimages: Jerusalem (in the Urban landscape, Urban continuity category), where Christianity started; and Vatican City (which does fall in this Religious Structure: Christian category, but sensibly has been broken out into a cathedral subsection by meltwaterfalls), home to the Holy See of the Catholic church.

As far as monuments go, I do think the Luther Memorials, as unimpressive as some visitors have found them, should get a mention because of their significance to the Protestant Reformation.

Routes of Santiago de Compostela (Spain)

I think we should explain our little green friend a bit about Christianity. That it is a belief followed by a significant number of the world population, which can be traced back 2000 years. That the followers see Jesus Christ as their prophet, a man born in Bethlehem at a site that still attracts his following. That the new belief quickly spread through the Mediterranean, leading for example to a 1st century house of worship in Damascus and Christian burial sites in Rome in the 2nd century. Over the years, the religion became institutionialized and a seat for their spiritual leader (the Pope) was created in the Holy See / Vatican City. In 1054, there was a first big split among the followers, which lead to a Roman Catholic group and an Eastern Orthodox group with their See in Constantinople (Istanbul). A second split came in 1517 with the Protestant Reformation, when Luther nailed his Ninety-Five Theses to the door of All Saints' Church in Wittenberg. Til this day, the religion atracts a great following in mainly Europe (as seen in pilgrims on the Routes to Santiago de Compostela) and Latin-America (to which it spread via missionary work, for example leading to Popocatepetl monasteries)

A lot of the other "Christian" WHS are actually on the List for their art or architecture, or are subdivisions of the main branches (or more examples of the same.

In bold the ones we seem to agree on. Italic the maybe('s).

Bethlehem - birthplace of Jesus
Luther Memorials - representing the Protestant Reformation
Baptism Site "Bethany Beyond the Jordan"
Kalwaria Zebrzydowska
Routes of Santiago de Compostela (Spain) - Catholic pilgrimage route that has been in use since the Middle Ages
Routes of Santiago de Compostela in France

That's pretty succinct -- I like it. The only addition I would suggest is "That Jesus was put to death and buried at Jerusalem, and, as his followers--called Christians--believe, rose again to offer eternal life to those who believe that he died for their sins." The inclusion of Jerusalem is important because of its importance to Christianity and its influence on world history (as the city has been fought over throughout its history), and a brief statement of belief should probably explain what differentiates Christianity from other religions.

Good addition, thanks. I am only in doubt which missionary site represents the spread to Latin America best.

In my opinion for this category we should not focus only for Christian as in my opinion the pilgrimage is the movement of a lot of people by faith which should be universal across religious, and WHS right now only the Routes of Santiago de Compostela seem to be the only single choice to choose. I don't want that when we go to Buddhism and we has no or less choice but to choose Japan Kii Mountains which is only a national level or Taishan for Taoism. WHS also really lack of sites with the Hajj in Saudi Arabia or great Hindu pilgrimage sites which seem more attractive for the little Green Man.

Yes, I second with Durian.