Capitalizing "Your" while leaving "passion" lower is called 'sentence case'. So, by finishing the sentence with the appropriate punctuation, hopefully I have made sense of things. My thinking is that "Your passion!" is referential (and subordinate) to "stir" which I see as the principal branding element - "stir" the business outfit and its offerings and the things talked about in its blog become the object of "Your passion!".
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