"Severe persecution" refers to the act of treating someone in a very harsh and unfair way because of their beliefs, opinions, or identity, often causing them great suffering or hardship. Full definition
The fourth century was a time of severe persecution of Christians in Persia under Shapur II. (religion-online.org)
One thing is certain — that it was written at a time of severe persecution for Christians and that it was written to encourage them to stand firm in the faith and to tell them of the future which God was preparing. (religion-online.org)
So far as we can ascertain the reason, it is to be found partly in severe persecutions which were visited on Buddhists as well as Christians and partly in the alien nationality of the Christians and of the Christian leadership. (religion-online.org)