So your answer is that this is the only way that you would believe that God exists?
What about all the people (93% of the world population) who already believe in God?
Do you think that God should communicate directly to everyone just because atheists cannot believe in God any other way?
Yes. Think of a loved one telling a unrelated friend to tell his husband he loves him rather than telling him, himself. While friends even good ones are well respected they don't replace the smile and care of the husbands themselves.
Yes. Especially when a person is in constant personal prayer, god tends to work through people say by the holy spirit. The holy spirit becomes the motive and interaction to which christians are bonded with the father through Christ. Without the holy spirit (or direct connection to god), jesus words mean nothing.
Go to the source to know if the messenger tells the truth. If the messenger agrees what you were told by the source by all means learn from the messenger. That's jesus message. Can't believe in Jesus if you don't have a personal and direct relationship with his father through spirit.
As for the other messengers, such as Moses and Muhammad, I'm not sure I'd they have a similar view of the holy spirit. I like their views better since they have a direct relationship with God and not the prophets as god himself. Even Muhammad says there is only one god and no person is part of god since god is one.
Messengers help to know about god. I can't read scriptures bahai literature the Quran, and Torah all day but means nothing without direct relationship with the author and not the ghost writer.