The following argument is sound (given Christian doctrine), where possibility and necessity are metaphysical throughout:
- It is possible to worship properly.
- Necessarily, worship is not proper when it is not of a maximally great being.
- Necessarily, worship is not proper when it is of a non-existent being.
- Therefore, possibly, someone worships an existent maximally great being. (1-3)
- Therefore, possibly, there is a maximally great being. (4)
- Therefore, there is a maximally great being. (S5 and concept of a maximally great being, as in ontological argument)
Here is a subsidiary argument for (1):
- All basic human forms of activity have proper functions.
- Worship is a basic human form of activity.
- Necessarily, when an activity fulfills its proper function it is being done properly.
- Any basic human form of activity that has a proper function can have that proper function fulfilled.
- Therefore, worship can have its proper function fulfilled.
A final comment. Dan Johnson has found a nice way to generate arguments like this one. You look for arguments whose premises are each either obvious or entailed by theism. This way, the arguments are guaranteed to be sound (if you think theism is true). However, nonetheless, there might be people who appropriately accept the arguments. Why? For one, maybe they have a left-over of a theistic conviction which they have irrationally rejected. For another, their sensus divinitatis might be telling them to accept premises like some of the ones about worship. Arguments like this will not appeal to a wide audience perhaps. They may appeal to a very narrow audience. But that is OK.