In J.R.R. Tolkien's fantasy novel The Hobbit, the dwarves gather at Bilbo Baggins' house because Gandalf told them that there was an expert "burglar" in the area "looking for a Job at once, and that he had arranged for a meeting here this Wednesday tea-time" (18).  Gandalf, of course, intended for Mr. Baggins to be the fourteenth member of Thorin's company on a hunch that Bilbo might prove himself an invaluable asset to the dwarves' expedition to the Lonely Mountain; in fact, the old wizard becomes quite frustrated when the dwarves question his wisdom in choosing Bilbo and defends his selection by asserting "there is a lot more in him than you guess, and a deal more than he has any idea of himself" (Tolkien 19).  

Bilbo had no idea of Gandalf's plans or intentions, so naturally the sudden appearance of thirteen dwarves on his doorstep at tea time befuddled the hobbit, especially when he believed to have only invited the wizard.  

Why do the dwarves visit Bilbo's home in The Hobbit?

In the classic fantasy novel The Hobbit by J.R.R. Tolkien, Bilbo Baggins (the hobbit) accompanies a band of 13 dwarves to the Lonely Mountain, their ancestral homeland, to recover their kingdom and its treasure from Smaug the dragon. Gandalf the wizard is responsible for bringing Bilbo and the dwarves together. He sees something special in Bilbo that he believes will make Bilbo a valuable companion on the quest to recover the treasure. Gandalf knows that Bilbo longs for adventure, even though during their initial conversation, Bilbo isn't even aware of it himself.

When Gandalf and Bilbo have finished talking, Bilbo goes inside in a huff, and Gandalf scratches "a queer sign on the hobbit's beautiful green front door." It is this sign that brings the dwarves together to Bilbo's home. After the dwarves have feasted on Bilbo's food and then cleaned up, Gandalf explains more clearly why he has had the dwarves assemble in Bilbo's home.

You asked me to find the fourteenth man for your expedition, and I chose Mr. Baggins. . . .If I say he is a Burglar, a Burglar he is, or will be when the time comes. There is a lot more in him than you guess, and a lot more than he has any idea of himself.

That's how Bilbo ends up meeting the dwarves and joining them on their many adventures.

Why does Bilbo join the dwarves on their journey in The Hobbit?

Bilbo never really makes a specific, definite choice to go on the journey; in fact, he spends a good deal of his time throughout the story thinking about how much nicer it would be if he had stayed home. 

Bilbo initially expresses no interest in going on any kind of adventure whatsoever, and attempts to usher Gandalf away, at least in regards to that subject. Later, Gandalf essentially lies by making a mark on Bilbo's door that identifies him as a burglar (which the dwarves were in need of) and the dwarves and Gandalf, from that time, treat him as such, regardless of his protesting (although at one point Gandalf has to clearly establish that Bilbo is a burglar because Gandalf says he is, which is a bit nonsensical but in keeping with the whimsical reasoning that keeps the book in a more lighthearted tone). 

The point at which we might say that Bilbo definitely "chooses" to go on the journey is when Gandalf comes to check on him the morning after the dwarves leave, and finding that Bilbo has not yet read their note, nor left to meet them at the inn, prompts him to go. However, Bilbo "to the end of his days" cannot remember how he committed to the decision. There is a strong suggestion that it was the "Took" in him, meaning the side of his ancestry that had a reputation for adventures and not being entirely "hobbit-like", meaning prone to rash decisions.

Why does Gandalf visit Bilbo Baggins' home?

Gandalf comes to the home of Bilbo Baggins to ask him to go on an adventure. His ultimate goal is to have Bilbo join the dwarves on their journey to Lonely Mountain, where they will have to defeat Smaug the dragon. Contrary to what Bilbo believes, Gandalf believes that the hobbit has both the mettle and courage to make the trip, and characteristics that will make him useful along the way.

The invitation to adventure is initially flatly refused by the hobbit, who considers adventure to be something that "makes you late for dinner." He makes it abundantly clear that hobbits live a simple life and "have no use for adventures."

When Gandalf mentions his former association with Bilbo's mother, Belladonna Took, Bilbo suddenly realizes to whom he is speaking and remembers the many wonders of which Gandalf is capable. It seems unlikely, initially, that Gandalf is going to get what he came for, because Bilbo is quite adamant that he does not want anything to do with an adventure, although he does invite Gandalf to tea the next day.

It could also be argued that Gandalf comes to the home of Bilbo Baggins to bring upheaval and surprises into Bilbo's life, which begins to happen when dwarves, instead of the wizard, begin arriving for tea the next day. Before long, Bilbo's home seems to be overflowing with dwarves, and by the time Gandalf arrives, the wizard has already succeeded in making Bilbo feel completely overwhelmed, whether or not this was his intention.