Richard Wurmbrand (1909-2001) was a Protestant Pastor in Romania where he was imprisoned and tortured for fourteen years by the Communist regime.
He left behind some invaluable words of advice for Christians contemplating a dark future - I pray they will never be necessary.
I append an excerpt, but, more than is usually the case, you need to read the whole thing.
H/T Dale Nelson
DOUBT MAKES TRAITORS
I am Jewish. In Hebrew, the language which Jesus Himself spoke and in which the first revelation has been given, the word "doubt" does not exist.
To doubt is as wrong for a man as it would be for him to walk on four legs – he is not meant to walk on four legs. A man walks erect; he is not a beast. To doubt is sub-human.
To every one of us doubts come, but do not allow doubts about essential doctrines of the Bible such as the existence of God, the resurrection of Jesus Christ, or the existence of eternal life to make a nest in your mind.
Every theological or philosophical doubt makes you a potential traitor.
You can allow yourself doubts while you have a nice study and you prepare sermons, and you eat well - or you write a book. Then you can allow yourself all kinds of daring ideas and doubts. When you are tortured these doubts are changed into treason because you have to decide to live or die for this faith.
One of the most important things about the spiritual preparation of an underground worker is the solution of his doubts. In mathematics, if you do not find the solution you may have made a mistake somewhere, so you continue until you find out.
Don't live with doubts, but seek their solution.