I read the other day how 2 thirds of American evangelicals don't believe in original sin, and a half don't believe in Jesus' divinity. This was used to support an argument that American evangelicalism isn't a set of religious beliefs, but a culture.
This got me thinking – this surely applies much more widely! I'd argue that actually a large majority of religious laypeople don't actually know what they believe. So how does this compare with years gone by?
I'm thinking about the 1300's – before the reformation, before bibles in native languages were used, how much did people actually know about their beliefs? Could a French serf take a break from his ploughing and explain to you the doctrine of original sin?
One of the chief arguments of the Hanbali/ Athari school of Islamic theology historically has been that it is the default theology of the masses, as opposed to the educated elite which had tended to subscribe to the Ashari, maturidi, or rationalist theological movements. The Hanbalis and Atharis argued that a person should not need to be highly educated to understand Islam at a practicable level, and that their theology was simple, intuitive, and straightforward enough for the average Muslim to understand, as opposed to other Islamic theological movements which placed a great deal of importance on underatanding certain abstract concepts which required the equivilent if a university level education.
Two well known historical anecdotes that highlight are the funerals of two famous Hanbali scholars: Ahmad ibn Hanbal (The founder of the Hanbali school) and Ibn Taymiyyah, which are said to betwo of the largest funerals in Islamic history. The funerals of these two scholars are significant because of the Hanbali narrative regarding how their lives were symbolic of championing an "intuitive" understanding of the Quran against a tyrannical government run by highly educated elites that believed the only correct way to interpret the Quran was the way that was taught in their University. Both Ahmad ibn Hanbal and ibn Tayymiyyah went to jail multiple times in their lives for their religious opinion, and the mainstream Hanbali narrative is that the story of their persecution reaonated very strongly with the average Muslim. Ahmad ibn Hanbal said that some of his biggest supporters were other prisoners- one of whom said something to the effect of "If I can stomach being jailed for my love of alcohol, then you can stomach being jailed for saying the truth about the Quran." To this day Hanbali preachers tell stories about how popular among everyday people Ahmad ibn Hanbal amd ibn Tayymiyyah were.
A couple of points on this, first on the Medieval era and then on a related Early Modern example.
The first point to say is that the medieval era was approximately 1,000 years (depending on where you set beginning and end points) - from around 500 CE to 1400 CE. Over that time, Christianity and its theology went from its initial empowerment and legitimisation by the Roman emperor Constantine, through the development of its various theological positions and differences and division into various versions (or heresies, depending which side you're on), through the conversation of primarily Europe and Scandinavia through the actions of influential individuals such as Boniface, through the establishment of the Papacy as a centre of power, the inextricable liking of Church and State (crowning of Charlemagne in 800) and beyond.
All of which to say, it really depends on which part of the Medieval era you're asking about. Christianity, Christian theological positions and heresies and the clergy's connection with lay beliefs changed massively over this time period. It's difficult to avoid generalising, but an overview can be given (and this is partly why I've included the Early Modern comparison further down).
Roughly speaking, during the Early Medieval era in Western Europe, Christianity was not in the dominant position we have come to know it for. Christianity had initially been introduced to Europe (I'm particularly thinking of France here) in the final decades of the Western Roman Empire. However, without the imperial infrastructure, this lacklustre conversion, originally centred in Constantinople, likely wasn't ever particularly influential in Western Europe and had very much lapsed by the time of the 7th and 8th centuries when rechristianisation began through the actions of individuals like Boniface and other eventual saints who trekked through the wilderness to establish religious settlements in strategic places (e.g. by roads or rivers). There are lots of saints lives from this time which involve this exact scenario. The infrastructure of Christianity was being created by intrepid individuals and driven from Rome, the bishop of which sought to take on one version of the Western Roman Empire's legacy.
During this early medieval era, the Church needed to negotiate both with political leaders (who would agree to conversion in return for political benefits) and with the local beliefs of individual communities. For example, Christian religious sites were typically built in the same place where the previous religious site had been (in an effort to both overwrite and blend the two). Lay understanding of church beliefs at this time was much more practical, as the Church's theological positions were being adapted and translated to convert the local population (Christianity didn't have the hegemonic supremacy it acquired later). Local religious centres also continued to serve other community functions, such as providing medicine and safe haven for travellers.
Translated Old English sources are particularly good for an understanding of lay engagement with theology. Recipes, cures and asking for God's help were much one and the same thing at the time. Continuing the theme of practical religion, lay people might ask for help with crop fertility, or with a lazy partner, or with health, or really any of the sorts of everyday questions we're still asking today.
The situation was very different in the Eastern Roman (Byzantine) empire, where certainly peasants in the capital would have been acutely aware of theological debates. Byzantine society was intensely theological as Constantinople was the centre of Roman Christianisation before the collapse of the West and it only continued from there. There were huge numbers of churches in the capital alone, many of which similarly served as community centres (e.g. healing your headache if you slept next to the saint's relics overnight) and religious leaders like John Chrysostom could wield huge influence and authority. Where religious controversies did happen (e.g. iconoclasm), it was very much a societal affair and the lay people were very much involved. God's favour was extremely precious to most/all Byzantines.
Later medieval lay understanding is a different question entirely. By that point, Church infrastructure and authority in Western Europe was firmly established to the extent that the Pope could now use theological rewards to send vast numbers of believers on ill-fated crusades. Theological debates had also become increasingly abstract and the preserve of the clergy, with the Church no longer having to adapt itself in order to negotiate and convert non-believers. The language barrier of using Latin (with the reasoning that it was the holy language) was also a source of socio-political power. This led to a state of complacency about peasant beliefs in Western European Christianity (Catholicism), culminating in the example of the 16th century Italian miller mentioned below.
It's also worth saying that Islam (which developed as an offshoot of Christianity in around the 6th century) did not have this language barrier issue as significantly because learning Arabic was a key part of conversion (or so I understand it - I know less about this than medieval Christianity). The only point is to further demonstrate the variation in the level of lay belief during that time period. It depends on geographical area, religion and the precise time period.
Recommended books include:
You may be interested an answer to an older question:
It’s a long post to begin with, and then we go back and forth talking about how to interpret a very specific piece of evidence (I think the most important evidence on the question). You can see she and I don’t fully agree how to interpret the various strains of evidence, but I think it’s one of my favorite discussions because it’s one of my favorite topics.