Faith used as a proper noun, is something unique to religion, evolved linguistically, specifically for use in religion and ideology. Religious or ideological Faith, is to be accepted as belief without reason or evidence and is ideologically indicated honestly by capitalisation of the initial F as it is in use a Proper Noun not a simple noun. This is comparable to "faith" the colloquial noun meaning trust or fidelity which is the more common usage. Confusing the two is a recipe for confusion and contention.
Since first and foremost Russell was a linguist he knew this and knew what he was saying.