Let me repeat back what I think I heard.
We have a lack of supply in housing. That's the main reason prices are so high across the country. To address this, we need to build a lot more housing very quickly. One of the ways we can do that is by making housing developments that previously weren't profitable for the developers, builders, etc. become profitable. The GST removal on purpose-built rentals is designed to make the construction of purpose-built rentals a bit more profitable. This means that a whole bunch of projects that previously weren't profitable and never would have happened are now going to happen.
Is that a good summary?