User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-32599925-20170717034056/@comment-32599925-20170719234918

In the original material, yes to being a messenger, a bit fuzzy on the first one. Technically, the original is some sort of "god-soul" that acts as the true god's hand upon earth, but it's also considered to be a god in its own right.

The Servant is a bit different. In this case, the 'god' is her hidden Noble Phantasm, and she isn't its messenger so much as it is a weapon that takes its form from her Origin. From the Servant's point of view, everything about her has been distorted by the aforementioned author.