Actually there are some similarities in gun ownership and worship. But it not in the way the artist portrays it here. It seems pretty clear to me that the artist is scornful of the concept of gun ownership and recognizing our inalienable right to keep and bear arms.
The similarities are that both are specific, enumerated, rights guaranteed to be protected by the U.S. Constitution. Both are essential for a free society to remain free. And of course both have cults, fringe leaders, have silly arguments over unimportant details like which is better a Glock after being baptized in the river, or a 1911 after being sprinkled with Holy Water.
If they would just think of us a religious group with gun ownership being the only criteria for membership in the church it would make things a lot easier and simpler for them to understand (I am not the first to suggest this but I can’t remember who I should give credit to). Simple is important because so often they have problems understanding even when you use simple words and concepts.
Imagine what that would mean: The Church of Gun would be the single largest church in the country, no taxes when you worship at a recognized range, and membership wouldn’t mean you were perfect–I would just mean that you were saved.