“the house.” Luke 5:29 makes it clear that it is Matthew’s house (called Levi in Mark 2:13-17, and Luke 5:27-30). Matthew was a tax collector, and so it makes sense that his friends were tax collectors and “sinners,” which is why so many people like that were at the dinner. This is a very good model of how to spread the gospel. Matthew became a follower of Jesus, and instead of starting to spread the Gospel by speaking with strangers, started by inviting his friends to a huge dinner and making sure Jesus was there to speak with them.
“Look!” The Greek word is idou (#2400 ἰδού), and it is used to get our attention. See commentary on Matthew 1:20 (“Look!).