The white blocks are like suction cups and I believe they are pulling the two blocks together here.
Later that day, the electrician showed up and while he was looking around he asked, "Is that oven going to fit? Sometimes you need to cut these up a bit..." I pulled out the installation manual and sure enough, I had to make the opening wider and taller. I panicked a bit and then went to Home Depot and purchased a jigsaw. I spent about an hour trying to figure out how to clamp wood to the cabinet to guide the saw, but in the end, I just marked the line and cut it freehand. I then had to lower the base that supports the oven and I did that rather quickly (and did not notice that I created a problem).
We got the oven in place, it was a beast to lift and the opening was a little short on width in the bottom, but we eventually got it. The cooktop went in fine, but the support brackets that are supposed to hold it in place don't fit inside the cabinet, so I'll have to put L brackets in their place. The Electricians put covers on all the outlets and since I have paint on the walls, Phase 2 is complete.