Stranger in a Strange Land is one of Heinlein's most popular books. And it is ambitious in many ways. It attempts to tackles the questions of love, and humanity, and evil, and the nature of God. And I can't say it really answers any of them, but I won't fault Heinlein for that.
No I'm not really sure what this book is to be honest. It's a piece from after Heinlein became a strong Libertarian, but it also carries notes of the man who worked on Upton Sinclair's campaigns. The book is essentially libertarian in nature, but also seems to conclude that the best way to live is in a small and completely free commune - though the book does question if this could ever work at scale.
And similarly, the book's treatment of women is strange. It certainly reinforces gender stereotypes and paints men and women as essentially different. But it prominently features many women characters, and I would venture to say all of the most most competent character's in the story are women. At its best, it makes it clear that men and women are perfectly and equally capable. But at it's worst - often through the viewpoints of the men - it supports the view of women as essentially sexual, enigmatic creatures.
Jealousy is a disease, love is a healthy condition. The immature mind often mistakes one for the other, or assumes that the greater the love, the greater the jealousy - in fact, they are almost incompatible; one emotion hardly leaves room for the other.
Similarly, you can see that book takes a strong position for western culture. It certainly takes its shots at every religion it can, but Jubal seems to always think that western society is doing things the best (though still quite poorly).
The religious takes are also often quite strange, and not always well thought out. Perhaps some of them are not fully explained, or take for granted cultural aspects that I am unaware of. Certainly the Fosterite cult, referenced throughout the story, is something of a parody of what people imagine religion must be like.
But perhaps none of the religious aspects should be put under too harsh a light, because it seems they all really exist just to give context to about the final hundred pages of the book. They aren't meant to stand on their own but rather to provide a backdrop against which to contrast the worldview of Valentine Michael Smith, the martian.
If you've got the truth you can demonstrate it. Talking doesn't prove it.
I think though, my biggest complaint, and what makes the book "just okay" to me, is that some of the elements at the end of the story just don't make sense. [SPOILER] When he continually cut to the angel Foster and Digby, I had no idea what was going on. I really felt like every single word of it could have been removed from the book and it would not have made anything worse.
All in all, it's one of those books that had just about everything there to be a really compelling read, but never quite put any of it together. Still I think it was worth reading, and I am glad that I finished it. But if you just finished Starship Troopers and want to read more Heinlein, you should probably look elsewhere.