The Holy Roman Empire WROTE the Bible.
They didn't just receive it from somewhere and then learn from it and apply it's teachings - they crafted the entire thing beginning to end - carefully organizing it, interpreting it losely, applying it losely, and overall instilling theirs values and beliefs IN IT.
They compiled a large collection of various books/letters that different subjugated and widely diverse groups/sects of believers had in their precious posession - and worked it into the book.
First, are you talking about the actual late Roman Empire or the Holy Roman Empire? They are not the same, and there is no political or social continuity between them. (aside from the religion itself, of course)
From the context of your post I'll assume you were discussing the late Roman Empire. Either way, such "top-down" alterations and synods were not a driving force behind the spread of christianity in the Roman Empire. Both the Council of Nicaea and St. Jerome's Vulgate (latin translation), for instance, were written after the religion had already been implanted throughout the empire.
Such top-down councils and decrees were responses to the widespread adoption and popularity of a religion already in place and already splintering into many separate factions and already generating a plethora of new scripture. Christianity spread through rome, not by the sword, but as an underground popular movement, which the Roman aristocracy had begun to accept (at least nominally) long before it was even an official state religion.
They also took many books and decided not to include them, as well - thus - the Lost Books of the Bible.
This has nothing to do with how christianity was spread for the first three centuries of its existence. The official canon was not decided until nearly three centuries after the religion had spread.
So - yeah they used it as a means to see to their political agendas, expand on their desires and centralize their power, grow their strength and spread worldwide - that's the whole point of the entire thing being in existence.
In the earliest years of the spread of christianity, it was not politically popular at all. It was, at best, political suicide for any aristocrat who adopted it-- and more often than not maybe
actual suicide. After centuries of its growing popularity with the non-aristocratic elements in society that changed, however, this was long after it had already spread and gained a strong foothold throughout the empire.
Alternatively, early Islam was spread by the sword and involved in the political suppression of other faiths... at least until it grew so large that its own internal divisions halted its advance into Europe, Asia, and Africa.