Unbelief is not having religious faith, or refusing to accept it. This is a church word, a Bible word, a word from sermons and theology — not a word for ordinary conversation. That is the first thing to hold on to. If you do not believe in God, you would say 'I'm not religious' or call yourself an atheist; you would not say 'I live in unbelief'. The people who use this word are usually religious people talking about the state of not believing, often with sadness or worry in the voice. In the Christian tradition especially it names a spiritual problem: something to be prayed about, wrestled with, healed. The most famous line in English carrying it is 'Lord, I believe; help thou mine unbelief' — a man who half-believes, asking for help with the half that does not. That line tells you the flavour: unbelief is not calm and confident, it is a lack, a gap, a failure to hold on. Note carefully that unbelief is not the same as 'disbelief'. Disbelief is the everyday word for the shock of not being able to accept something you have just been told — you stare at someone in disbelief when they say the shop has closed down. Unbelief is about faith, and it is a settled condition rather than a moment of shock. It is an uncountable noun, so no 'an unbelief' and no plural.