I've mentioned this in a couple of posts, but it seems to have been bypassed, so I thought it might be a good idea to start a thread on it.
Roman Catholics and Orthodox Christians believe in the intercession of the saints. They communicate with people who have passed away and ask them to pray (or intercede) on their behalf.
My argument is that only God is omnipotent. When many people try to speak to Mary, for example, all at the same time - she cannot hear everybody at the same time, therefore it is impossible to know who received her message and who didn't.
As demons have been known to impersonate real people, then trying to communicate with those who have passed away is a dangerous thing to do. I believe that God forbids it:
10 There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch.
11 Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer.
12 For all that do these things are an abomination unto the Lord: and because of these abominations the Lord thy God doth drive them out from before thee.
That is why people should not be talking to St. Anthony, St. Francis or even their dead grandmother. This is the same as spiritualism which I also believe is a heresy.
Also, there is only one meant to be one mediator and that is Jesus Christ, so why pray to anyone else or ask anyone else?
Intercession, I believe is only for the living, by the living. I can ask you to pray for me and you can ask me to pray for you. There is no reason to ask a deceased relative to pray for you - in fact I believe that it would be wrong to do so.
Unless of course, I am wrong and it is not only God who is omnipotent!