It’s not because “those are our rules.” It’s because we believe our religion is actually true.
That’s the long and the short of it. And as shocking as the concept might be in a postmodern age, the fact that our religion is true makes others false inasmuch as they contradict ours.
If we are correct, then the consequence is that when Christians stand up and preach, we are not doing the same thing that pagans are doing when they stand up and preach. Pagans might make people feel better. Pagans might offer emotional comfort in times of distress. Pagans might foster a sense of unity in a community in the face of a shared tragedy and help people get a sense of closure and move on with their lives. Christians also might do these things when they stand up and preach, but they are only doing these things because they are actually telling people what God has actually spoken. Christians might offer words of comfort to those who are grieving. However, those words are only comforting because they are actually God’s promise of salvation through Jesus Christ.
Any atheist can tell you that these prayers, homilies, and assurances are hollow if they are not true. The pagans’ are not true. The Jews’ are not true. The Muslims’ are not true. The Christians’ are true. If you want to take issue with that by saying that Christianity is false, then that’s fine. Many of us would be happy to go over the evidence that demonstrates how you’re wrong. But don’t expect us to blithely stand up with pagans and pretend that what we’re doing is the same thing as what they’re doing. It’s not.
This might rain on your parade. It might stymie your plans to provide emotional comfort and community unity. So be it. God’s promise of grace to all who believe in Christ is more important than community unity. It is more important than a sense of closure. The Gospel we have to offer is the power of God unto salvation. We will not cheapen it by likening it to what the pagans have to offer.