After King Alfred the Great defeated the Viking King Guthrum, Guthrum underwent baptism to Christianity as a condition of surrender and treaty.
The modern mind wonders whether such an apparently compelled conversion would have any meaning; and whether Guthrum was cynically pretending as he went through the ceremony.
By my understanding; the mind of men of the Dark Ages did not work in that way. Modern Men cannot help but detach their actions (such as religious rituals) - from what they 'really' think.
Modern Man divides the subjective state of mind, from the external and objective.
But ancient Men's minds worked differently. For them, subjective and objective were not fully divisible; therefore ritual had an objective effect.
The Christian martyrs of ancient times sometimes died rather than speak words that would deny Jesus, or burn incense to another God - this emphasizes that they could not and did not distinguish between word/ action and belief. If the martyrs had denied Christ verbally or participated in a false ritual - then they really would have been de-converted.
Coupling of (what we now think of as) subjective with objective, dwindled through recorded history; but there was a residual linkage until the past few generations.
For example; the speaking of an oath to tell the truth in a law court was regarded as an effective way of ensuring that truth was indeed spoken. Few would believe in the power of such an oath nowadays.
This psychological fact-of-life was bound-up with the structure and function of churches in all the religions - and its dwindling, and now absence, is a major factor that underlies the collapse of 'institutional' Christianity - the inability of churches to compel doctrine, behaviour, allegiance, loyalty, obedience.
It cuts both ways:
On the one hand, modern Men cannot be converted to Christianity against their will: conversion is necessarily a choice. A modern Guthrum would need actively to want to be a Christian, to become a Christian.
On the other hand, modern Men cannot be de-converted from Christianity by compelling them to say certain words or do certain things. A Christian would not lose his faith 'merely' by denying Christ or burning a pinch of pagan incense - for de-conversion to be real, such actions would need to be motivated by anti-Christian convictions.
Modern Man has become immune to 'the sacred' - he cannot rely-upon 'the sacred' to induce a 'Holy' response in himself. On the other hand; the widespread and purposive, whether casual or malicious, desecrations enacted by the evil totalitarian System will surely sadden him, but they do not annihilate his capacity for faith.
We are now personally responsible for our Christian faith - like it or not; there are neither compulsions nor excuses; the church can neither make-us nor break-us.