What's the purpose of this holey wall?
Solution 1:
It's related to one of the hidden stars in the game:
You can use the painting from level 3 to create a star, and use the platform from level 2's painting to get up into that space to collect it. Unfortunately, you can't get this star after finishing the level 3 painting, so you would have to restart to get it. You can find more information here: http://strategywiki.org/wiki/Braid/Stars