This page is dedicated to discussion on the topic of the ‘windows of heaven’ – arrubot hashamaym and related expressions. I do have material on this topic that I have not published yet, in answer to commenter Mako. Until then Mako made some terrific points. I would note that it is important to not treat this expression in isolation from some other related expressions (like ‘treasuries’ or ‘storehouses’ of heaven). Cheers!