I used to think having many rooms in the Father's house was a reference to marriage or adoption. If someone wanted to marry a woman while staying in their father's house, they had to provide the bride with a room. Of course if you're going to adopt a child, you need to give them a room. I have recently learned that all of that isn't even the point. The point is that the body of believers IS the Father's house. It's ultimately trying to say that you are a room in the Father's house. God wanting to marry or adopt us is great, but it's even more intense to see that he wants you to be a room in his house.