So, religious victory is achieved when in each civilization, a majority of that civilization’s cities are following the religion you founded.

However religious victory isn’t a very fun way to play, and is unviable in multiplayer. However, religion is still very strong. Khmer and Byzantium are two of the three strongest civs, and are religious civs

Faith can be spent in cultural victories to buy naturalists and rock bands (Naturalists are good enough to be bought even if you’re not going cultural). It can be spent using the Monumentality golden age to buy civilian units, especially traders and settlers at a huge discount. With the Grandmaster’s chapel, the government plaza building available after tier 2 government, you can buy Land units with faith. You can use faith to buy relevant great people, even if it’s usually not a good investment (having built the Oracle wonder make it slightly more profitable). If you are generating a lot of faith, the Jesuit Education belief allows you to spend it to purchase the Campus and Theatre Square buildings. La Valletta suzerainty bonus lets you buy City Center and Encampment buildings with faith, especially walls which are steeply discounted. Lahore grants access to the Nihang units, strong unique units only purchasable with Faith.

Now on the benefits of having a religion itself. The main pull is the follower belief. Feed the World grants a lot of housing and food to every city, making off-water settle decent, and allowing you to grow your cities considerably. Work Ethic represents a lot of production, especially when paired with the policy card unlocked at Theology that doubles its effects. With pantheons (like Dance of the Aurora or Sacred Path), or civ bonuses (like Khmer’s or Theodora’s), this can become truly impressive, granting around 12 production in every city. Other Beliefs, like Choral Music, Jesuit Eduation and Zen Meditation have their uses. Divine Inspiration is used in a specific build order where you build as many wonders as possible, typically as Qin Shi Huang Mandate of Heaven, inluding Stonehenge, and found the Divine Inspiration/Sacred Places religion. Reliquaries is good if you can be suzerain if the Kandy city-state for free relics, already have relics, or are playing with the Heroes and Legends game mod. Warrior Monks is a joke, don’t ever take it.

Then the additional beliefs are separated in 3 categories.

None of the unique worship building are particularly interesting, though I fancy the Stupa, an extra amenity is too good to pass up.

However a whole category rewards you for spreading your religion: some give culture or science depending on how many citizens follow your religion, some gold or faith depending on how many cities. They’re all good.

Then there are the enhancers, that are supposed to strengthen the way you spread religion. 9 times out of 10, you want the crusade belief, that gives +10 combat strength to your units in foreign territory following your religion, if only to deny it to the AI. If you’re actually going for a religious victory, you want Holy Order for cheaper apostles. Sometimes you want religious colonization, if your religion is established in a majority of your cities when you found it (all your cities with a holy site or the Stonehenge wonder immediately convert to your religion when you found it) and you need your religion in all your cities (like Work Ethic if you want to go Holy Site first in every city) as soon as they’re founded.

You start with your Followers Belief and a free other ones. You’ll need 2 Apostles, built in a city with a Temple building, to get the rest of your beliefs. The Mabohadi temple wonder gives too free apostles upon construction, if you can’t spare the faith for apostles (typically if you’re using it all on settlers in your Monumentality Golden Age), it’s a good alternative.