Kaika...all I can say is keep your temper in check, there is nothing you can do to make your parents less annoying. When religion walks in the door common sense flies out the window.
Unless they begin trying to convert you into thier beliefs, leave them be. Find other things to do or think about that can take your attention away from it for awhile. Getting upset with them really isnt going to do anything but elevate your blood pressure.
As I've gotten older I've seen this sort of religious conversion in people as they begin to grapple with age and thier own mortality. The more immersed in it they become, the less aware they are of those around them dealing with real issues. My own stepfather has been a "born again" for many years now and it was nearly impossible to be around him for more than a few minutes at a time before the preaching began. My mother noticed how I would cut my visits short when he started and I had to be honest and tell her how uncomfortable it made me feel, I wasn't there for a sermon or religious debate. I just wanted to spend some time with them. Things are better now, they both know if they dont want me around all they have to do is begin preaching the gospel and I'm outta there.
The only thing you can change is your reaction. Accept them for who they are and what they believe but set some boundaries for yourself. Have you spoken to them about how you feel?