TL;DR
An early sect within The Church of the Holy Mother made a pact with the patriarchy. This sect surrendered their claims to political power to the patriarchs and in return the patriarchs recognized the sect as the sole legitimate religious authority. As a result, having celibate, cloistered women running the church and working as advisors eventually became tradition.
luizpsr provides a great justification for the contemporary position of The Church of the Holy Mother: woman yield religious authority but let men take care of mundane matters. For my answer, I'm going to look into how this arrangement could come to be.
Side Note: My use of "church" as opposed to a "cult" is intentional.
Historical Examples in the Real World
Common Trends
If you look at the history of various religions (including Christianity), you'll see some trends:
- After the initial emergence of the religion, a wide variety of interpretations and traditions develop and then begin competing to shape the religion's orthodoxy.
- In order to spread, religions often adopt some values from the existing cultures.
- Religious organizations often provide secular leaders with legitimacy and a good reputation in exchange for material support.
#1 and #2 both explain why religions may seem contradictory; they aren't just the continuation of an initial revelation, but the on-going process of reconciling differing interpretations. #3, meanwhile, explains why religious organizations may compromise their ideological purity. In other words, a (nominally) matriarchal religion operating within a patriarchal society is not only plausible but realistic.
Paul & Thecla
A specific historical example that is especially relevant involves the Christian Apostle John and a woman named Thecla.
According to the Acts of Paul and Thecla, she was inspired by Paul's teachings to convert to Christianity and leave her fiancée for a life of celibacy. The stories depict Thecla enduring numerous trials - including miraculously surviving multiple attempts to execute her - before becoming a preacher. These texts also reference other female preachers and depict Paul as an egalitarian and strong advocate for celibacy.
By contrast, the Pastoral Epistles depict Paul advocating for women to serve a subordinate role in the Church and dedicate themselves to raising children. Though evidence is limited, it's likely this contrast was intentional. The Acts of Paul and Thecla and the Pastoral Epistles reference people and events that are rarely mentioned in other Christian texts but promote opposed ideologies.
Despite Thecla being widely known and venerated until at least the 4th century AD, the Acts of Paul and Thecla did not become canon, but the Pastoral Epistles did. This suggests that those promoting traditional gender roles prevailed and became part of mainstream Christianity.
(This video goes into more details about Paul and Thecla.)
History of The Church of the Holy Mother
Using the observations and examples above, here's a proposal for a history that would explain how The Church of the Holy Mother developed over time.
The Time of the Founders
Though the nation now has a unified political system and culture, in ancient times, it was home to a variety tribes. They differed in many ways, including gender roles; some were completely male dominated, others were completely female dominated, but most were somewhere in between. One of the few things these tribes did have in common was a prophecy in which a virgin woman would give birth to the Messiah.
The Messiah was born into a tribe that was effectively egalitarian. The people of this tribe were willing to accept a man as their leader, but also comfortable with the role The Mother of the Messiah would play. For while the Messiah was as wise, charismatic, and ambitious as his mother, he lacked her passion for theological debate and her skill with managing organizations. He dedicated his time to preaching to the masses, socializing with benefactors and allies, and eventually leading armies; he entrusted his mother first with organizing his fledgling religion and later with managing many domestic affairs of his burgeoning empire.
As a result, both the Messiah and his mother became influential and widely respected. However, the Messiah led a much more public life, leading to him being the better known of the two. Both his triumphs and failures were on display for the world to see, as were his virtues and faults; despite being revered, he was too human to convince most people that he was purely divine.
By contrast, the Messiah's mother maintained an air of mystery. Her interactions with the public at large was limited. Instead, she was known through her writing - which she produced a lot of. This included letters communicating on behalf of her son, chronicles of her son's exploits, and treaties establishing the basic precepts and lore of the then-new religion. Establishing herself through words and not deeds allowed her to maintain a more pristine reputation.
Struggles between Early Sects
Though the Messiah succeeded in establishing his political power and passing it on to his heirs, it was his mother who ultimately came to dominate the religion. After her passing, other women close to the Messiah continued in her footstep. However, each had a different relationship with and understanding of the Messiah and his mother; it was from this that many sects formed.
Key points of contention included:
- How much of the Messiah's success could be contributed to his mother? Was she just moral support or was the Messiah just her proxy?
- Did the Messiah's mother have any romantic or sexual relationships or did she remain chaste?
- How involved was the Messiah's mother in daily affairs? Was she an active, engaged leader or a reclusive, detached theologian?
According to one sect, which I shall call The Brides of God, the Messiah's mother lead through inspiration but was detached from the mundane world - avoiding politics and remaining celibate. This sect was primarily composed of women who preferred a life of intellectual enrichment; many choose to be cloistered and celibate to focus on spiritual purification. Among other things, this sect wrote famous texts on how to properly organize society and established the practice of holy matrimony to God.
The Bargain that Established Orthodoxy and Canon
The competing interpretations among various sects was aggregated by rising political instability; the Messiah's male descendants did not hold as much influence, particularly among those tribes that were traditionally led by women. This proved to be problematic for a group of elite patriarchs whose forefathers had amassed power through good relationships with the Messiah. They were concerned that there position would be compromised if the Messiah's descendants lost power or were forced to make compromises with the matriarchs.
Meanwhile, The Brides of God were struggling. First, sects that had encouraged woman to have large families proved far more capable of maintaining and gaining adherents over numerous generations; these sects were gaining more influence as a result. Secondly, The Brides of God had originally benefited from the support of prominent matriarchs whose daughters, sisters, and mothers had entered into holy matrimony. Over time, though, this support waned.
Fortuitously, the people within the two groups knew each other and conversations began that eventually led to an unspoken agreement. The elite patriarchs would provide the financial and logistical support The Brides of God needed. In exchange, The Brides of God would craft a compelling argument to counter growing distrust and resentment towards the patriarchs.
This plan proved so successful, that The Brides of God soon overshadowed all other sects. Using their political power, the patriarchs officially recognized the traditions of The Brides of God as orthodoxy; The Brides of God became The Church of the Holy Mother. Though many other sects were brought into the fold, it was The Brides of God who had the final say. In particular, they established religious canon, ensuring that any texts or teachings that opposed the patriarchy's right to rule were deemed unacceptable.
Story Telling & World Building Benefits
Using the above in your world building I feel offers a lot of benefits, including:
- It provides an opportunity for a rich, diverse culture with variations across different regions and social groups instead of a homogenous, monolithic culture.
- It provides the nation with a deep, dynamic history that's more realistic than one that came into being and somehow stayed the same for centuries.
- It provides the background for a realistic religion with a lot of idiosyncrasies, apparent contradictions, and differing interpretations.
- It provides a rich source of tension and conflict between the church and state; due to ideological differences, both would be motivated to help the other only as much as necessary and would likely have many subtle or overt attempts to exert influence or take power from the other.
- It allows for multiple explanations for the irregular pattern of new god-emperors emerging. Supporters of The Church of the Holy Mother would see it as necessary to renew the faith of the people and the strength of the nation against the forces constantly seeking to end peace and prosperity. Opponents of the church would suggest that the births were not holy or virginal and instead a ruse to maintain power. Both could claim to be fighting against corruption, allowing for antagonists that aren't just acting for evil or selfish reasons.
In summary, instead of having a simple explanation for the apparent contradiction between religious matriarchs supporting male rulers, my advice is to develop a more complex one that can be leveraged for richer world building and more nuanced conflicts in the story telling.