Why do we say Rest in Peace RIP?

Have you ever wondered why we say "Rest in peace" when someone dies and at a funeral?  I was asked why by a child the other week and I can honestly say I've never really thought about it before.  I think I provided a semi coherent response including an admission of not really knowing, but it left me wanting to know a little more.



Is it referring to death being the final rest for the body as the soul goes to heaven?

Is it from the days of grave robbing when you literally asked God to let the dead rest in peace without disturbance?

Is it a modern day translation of the letters R.I.P which in latin was Resquiet Im Pace.  This was used in Britain in medieval times and was commonly referred to during the Black Death.  The plague killed people in agony and the inscription was a reassurance that at last the dead were at peace.  

Is it referring to the old testament understanding that death was a great sleep from which you could be woken?

Or perhaps a reference to the catholic concept of waiting for judgement from God at your death?

Maybe it's a call to the mourners that we try to accept our loved one is at peace and resting.

Or it might be a reference to the fact that torture is now ended as heaven provides rest and solace for the soul.

On the other hand it could be that we rest in death until Christ comes again and we are all renewed in life.

I don't know and I can't find any definitive answer.  But what I do know from this research is that it is a comfort for us that remain behind to wish our loved ones peace and rest everlasting.