Here are your claims - dynamic, atmospheric, demands immersive roleplay, highly believable world, poignant themes...
A good marketing blurb tells the potential customer what this is, what it includes (generally the good stuff to garner interest), and why it's different. Also, a good marketer doesn't have to tell you how to think about their product. They can describe it, sell it, and evoke those thoughts and feelings from the audience.
...
What is this Souls Calling game? Tell us something about the setting. Tell us something unique about the game. What do the characters do? Why is this setting different or unique based on the settings available out there? Excite me. Make me want to jump up right now, make a character, and play your game.
...
OK, let's think. Bullet points of what's included as per Flying Mice. This will have to be considered a work in progress...
* an immersive tabletop roleplaying game set in the Enshrouded Lands
* where knights, peasants and priests alike know nothing of the eldritch,
* but the world teems with secret magic, hidden terrors and occult fantasy
* take the part of one of the bold few chosen to behold these mysteries
* the ref reflects your alter-ego's persuasiveness and empathy in his roleplay
* that method depends on direct speech - you have to speak AS your character to speak FOR him
* dialogue is never interrupted to roll dice about dialogue
* combat can be handled impressionistically or in detail
* the rules are structured around d12 + stat v d12 + stat roll-offs
* your character's abilities are balanced around his best way of tackling the challenges of adventuring - close quarter combat, ranged combat, stealth, persuasion or eldritch talent
* the Fates reward those who stay true to themselves
* but your cosmic masters reward you for answering your Soul's Calling
* and you can opt in to incentives to toy with your fellow players
* huge flexibility of CharGen and magic system
So - how's that?