Thanks to MandM for these quotes –
Augustine says (Tract. xxvi in Joan.) that “it is possible for a man to do other things against his will, but he cannot believe unless he is willing.” Therefore it seems that unbelievers ought not to be compelled to the faith. – Thomas Aquinas
Lactantius, a 4th century theologian,
I should wish to know, when they compel men to sacrifice against their will, what reasoning they have with themselves, or to whom they make that offering. If it is made to the gods, that is not worship, nor an acceptable sacrifice, which is made by those who are displeasing to them, which is extorted by injury, which is enforced by pain….These things may indeed be said with justice. But who will hear, when men of furious and unbridled spirit think that their authority is diminished if there is any freedom in the affairs of men? But it is religion alone in which freedom has placed its dwelling. For it is a matter which is voluntary above all others, nor can necessity be imposed upon any, so as to worship that which he does not wish to worship. Some one may perhaps pretend, he cannot wish it. In short, some, through fear of torments, or overcome by tortures, have assented to detestable sacrifices: they never do that voluntarily which they did from necessity;
And finally Tertullian a 2nd century theologian
It is a fundamental human right, a privilege of nature, that every man should worship according to his own convictions: one man’s religion neither harms nor helps another man. It is assuredly no part of religion to compel religion— to which free-will and not force should lead us— the sacrificial victims even being required of a willing mind. You will render no real service to your gods by compelling us to sacrifice. For they can have no desire of offerings from the unwilling.
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