The consistent use of the Decalogue in the rite is one of the peculiarities of our common prayer. Probably borrowed from the Strasbourg liturgy, it allowed Cranmer to move further away from the overtly Roman model of 1549. But, in all events, this oddity has pretty much disappeared altogether, wherever you go. Why it ever rose to prominence, in the first place, is the question.
The "Ten Words" had been purged from Jewish liturgy by rabbinic Judaism. And they weren't of much interest to Western Christianity -- intent on touting its own superiority to what came before -- until around the twelfth century. Why it began to emerge from the shadows is a mystery, although one can point to any number of possible factors, social unrest and the rise of mandatory confession being only two of the most prominent.
Aquinas had written:
Three things are necessary for man to be saved: (1) knowledge of what is to be believed [scientia credendorum], (2) knowledge of what is to be desired [scientia desiderandorum], and (3) knowledge of what is to be done [scientia operandorum].
The first is taught in the Creed [symbolo], where knowledge of the articles of faith [articulis fidei] is given; the second is in the Lord’s Prayer [oratione dominica]; the third is in the Law [lege].
This has the form of the practical syllogism: P1 = belief, P2 = desire, and C = action. But these three areas are here further circumscribed by what we should believe, what we should desire, and what we ought to do.
(1) Belief is regulated by the Creed (and the Articles of Religion). These say nothing about demons or witches nor indeed of any form of personified evil. What we believe is characterized not by gloom and despair but by hope and expectation. It is a synopsis of the content of the Good News.
(2) Legitimate desire is articulated by the Lord's Prayer, in which we are told we may ask only for four things:
Your kingdom come;
Give us (each day) our (daily) bread;
Forgive us our sins;
Save us from the trial.
We don't need anything else. And hence we are now and radically free.
From these two things alone, (3) right action should (ideally) follow. But it would be good to have a crib sheet, just in case. Fortunately, we have two distinct glosses -- one positive, the other mostly negative -- that nonetheless neatly correspond.
"Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength."
- Thou shalt have no other gods before me
- Thou shalt not make unto thee any graven image
- Thou shalt not take the name of the Lord thy God in vain
- Remember the sabbath day, to keep it holy
- Honour thy father and thy mother
"Love your neighbor as yourself."
- Thou shalt not murder
- Thou shalt not commit adultery
- Thou shalt not steal
- Thou shalt not bear false witness against thy neighbour
- Thou shalt not covet
The laws of worship and piety and the laws of charity and justice. Pretty simple really. This is the love that can be commanded: it is called respect. It is an attitude, a comportment -- not a feeling.
Another way of parsing it all: the law of belief comes from the Church; the law of desire from the New Covenant; and the laws of action from the Old Covenant. But, once again, why weren't the first two alone sufficient?
That comes clearer from a third way of dividing up the territory: belief concerns the individual; desire the family and the (near) neighborhood [the particular]; and action the stage of the greater society or nation [the universal]. And so we would do well to acknowledge the following state of affairs:
The late medieval era therefore gave rise to wave after wave of reformers who called for instruction, social discipline, and the establishment of order.
Under such circumstances it made a whole lot of sense increasingly to turn to the Old Testament as a guide. Unlike the New Testament, which was written to congregations of individuals and families who had voluntarily embraced their calling to be separate from the broader society, the Old Testament was written to a nation of millions, steeped in idolatry and pagan practices, kept in the faith in large part by political authorities. Unlike the New Testament, which could assume a thoughtful devotion in response to grace on the part of Christ’s voluntary disciples, the Old Testament used rewards and punishments to curb idolatry and promote righteousness. Unlike the New Testament, which emphasized teaching and growth in maturity, the Old Testament featured the prominence of ceremony, pageantry, and symbolic instruction at the hands of a select priesthood.
In these ways and so many others the medieval church found its situation to be far more analogous to that of ancient Israel than to that of the early church. It was probably inevitable, under these circumstances, that the Old Testament would increasingly become the paradigm for the life of the medieval church. Reformers increasingly demanded decisive action on the part of those with power, looking to Israelite kings as examples. They called for the authorities to extend their coercive power over institutions and realms of life not previously subject to temporal authority.
In a word, political realities demanded a re-emphasis of the Old Testament. In particular, the Decalogue provided the appropriate medicina mentis of the moment. That time will not come again, no matter that the final upshot remains in force: "reformers" demanding the government to extend its coercive power over every aspect of ordinary life. The rest of us? Back to the bunker.