Someone you cared for has passed away and the funeral will be an overtly religious one. As a nonbeliever yourself, you feel uncomfortable about attending this type of funeral. Should you still go? What constitutes polite behavior if you do decide to attend?
Your Two Best Options
If you dislike the idea of attending a funeral that will be a religious service, consider making an appearance at the visitation or wake beforehand and leaving before the service begins. Not everyone who comes to a visitation stays for the service.
However, if you can override your feelings on this issue, the deceased person's family will appreciate your presence at the funeral as well.
The worst thing you can do is not appear at all, even if you send a card and flowers or a monetary gift. Unless you have a completely valid reason for not going -- such as not being able to get off work -- at least stop by for a few minutes and offer your condolences.
If You Go to the Funeral
You do not have to participate in any of the rituals even if you're in a church and there is a religious service. You also do not have to call attention to your disbelief. Being quiet and respectful as people sing hymns, recite liturgy or creeds, or pray as a group is acceptable.
Do follow the group's actions as far as standing and sitting. If the service is one during which people cross themselves, kneel or receive Communion, nobody expects you to do this if you're not a member of the denomination. In fact, many churches consider receiving Communion outside of one's own denomination to be bad form.
Depending on the church, there may be another possibility offered during Communion. Guests may be invited to walk up with everyone else and receive a blessing instead of the Sacrament. However, as an atheist, you may not want to participate. You probably won't be the only one who remains in your seat, since people of various religions -- and of no particular faith -- commonly attend funerals together.
The family will appreciate your presence at either the visitation or the funeral service -- or both. You don't have to compromise your beliefs by attending, and you can still be courteous while abstaining from certain rituals. People will probably not be paying attention to you during the service anyway, since they are there to cope with their grief and offer support to the family and close friends of the deceased person.