Pibemanden is essentially correct. Due to mechanics, it looks like a spell is being cast upon a person. However, in execution, it is simply no more than a cleric silently asking his/her deity about another character and getting back one of five possible responses: Allied, Friendly, Neutral, Unfriendly and Enemy.
If the "target" character does not have a deity, the response always comes back as Neutral.
Also, it is very correct for a cleric to use this to determine whether or not he/she should travel with or openly aid another character. We take the relationships between deities very seriously here, and so do the deities themselves. Clerics, Paladins and Champions need to be very aware of who they aid. Their deities do not long tolerate the use of their blessings upon those who follow their enemies.
We have, in the past including two incidents pretty recently, taken powers away from divinely-empowered characters for a practice of aiding followers of enemy and unfriendly deities.
One last thing: It's very important for everyone to remember that when a divinely-empowered character refuses to travel with or aid someone on the basis of deity, this is an IC response, not an OOC one. Keep in mind that it is the character properly portraying deity relationships, and it should not be taken personally in an OOC sense as the player refusing to help another player.
