It means "exact" - it's not necessary, but adds emphasis to the statement. So, in this sentence, the speaker wants to draw special attention to the fact that he was born in THIS house.

when we say "in this very (place)" it is for emphasis It means that something special happened or will happen right here. We say with with some excitement or exclamation, because it is special/interesting/exciting to visit this place it is very similar to using "RIGHT here" "in this VERY spot" here are some examples: - At this very spot, Tiger Woods broke the record for .....! - In this very location, a meteorite hit the Earth 2 million years ago! - Right here, in this very spot, Abraham Lincoln was shot dead! - They will build a new skyscraper in this very spot! - I will build a house and raise a family in this very spot. ....or it might not be a special event, it could just emphasize "exactly here" - Let's meet back here, in this very spot, 2 hours from now. hope that helps :)

'very' here is used to emphasize how important the house is. 'very' has different meanings as both 'adjecitve' and 'adverb'. It could emphasize the importance or seriousness of something. In your example: "It was in this very house that he was born." It means in this specific house referring to the significance of this house and its relation to something mentioned in the context before.