Back to the topic.
Clerics, Druids and Paladins are the way to go if you want your players to treat the gods seriously. In one of my early campaing in the second edition, one group decided to ignore the god one player had chosen (Chauntea). They were clearly in favor of an other god and the cleric's player was disappointed about that. But one player was particularly adamant on his faithlessness.
He started to thank Chauntea for every spell he was given and slowly as time went on, his spells were having less and less effects on the unbelievers and were functioning at full power on the faithful in the group. As it was doom to happen, one of the unbeliever died. As he tried to raise him from the dead, Chauntea appeared in a shared vision between the faithful (but in front of all players). The encounter went approximately like this.
-Why do you want to bring back that faithless soul to your world? Has he not mocked you and Me enough?
-Goddess, he's a force for good. He should be brought back to continue the fight against the evil roaming this land.
-Your forgiveness is a boon to your dedication to your friend. But I see no reason for me to bring him back beside pleasing you. You have been very tolerant of him. Too tolerant for my taste. I shall not bring him back because he mocks ME and MY church. You are one of my favorite, but your friendship with that faithless soul has blinded you to the obvious, He does not believe. Only true believer can receive my blessing. And only if they are furthering the goal of my church. He has had his chance. He decided to mock your beliefs and your church. He shall not be brought back by anyone of my church. And be warned, I want him to go to the after life. You do not mock a goddess with infinite impunity.
The goddess disappeared and the players immediately searched for an other religion to bring him back. The cleric was giving a lot of money to bring him back and he was doing a lot to bring the faithless back. No church wanted to bring him back as the faithless was just that, faithless. They finally found some cleric of Waukeen ready to raise him for quite a substantial amount of money (6 times what was normally recommended). As the faithless was brought back. The cleric of Chauntea lost his spell casting ability.
He found someway to communicate with his goddess through an other cleric of Chauntea.
-I told you I would not like to see your faithless friend brought back. You did not listen. Now you will have to atone for your digression. Your friendship is admirable. Your devotion less so. But as your goddess I give you this chance. Make him a faithful of our church and do a quest this cleric will give you. All earnings of everyone will go to the poor. Only then shall you recover more than 2nd level spells (character was 11th at that time).
The faithless became a faithful of Chauntea, helped the cleric atone with quite a quest and from then on almost all my players have had quite a respectful stance on the power of religion in game.
I simply felt like sharing a small story that happened in one of my games.
Hope you enjoyed and that it will help you.