The phrase “windows of heaven” in 2 Kings 7:2 pictures God’s provision as being more than one person or even many can cope with. It is used by a king’s unbelieving advisor to mock the possibility of God reversing a city’s plight from starvation to plenty of food for all in just 24 hours. (“As if!”) But, lest we think of it only as an expression of unbelief, the prophet Malachi uses it positively to promise God’s blessing on those who tithe (Malachi 3:10).
Not that heaven has windows that God opens to provide for His people. In the first instance the food was found in tents abandoned by a terrified enemy army. Which brings us to Luke 6:38 and the well-known “good measure, pressed down, shaken together, and running over” reference to food, which Jesus said that those who gave would receive in the same measure they used to give. (In those days, wheat and other grain food was measured out to buyers from sacks.
So the phrase “windows of heaven” speaks to us of God’s provision for us from heaven, given in the measure that we give or bless. Those who give generously receive more than enough for their needs. Which is seen on our earthly level, cyclically, through our support for those “out there” in ministry, breaking new ground (Philippians 4:15 & 19).
That said, we need to bear in mind that a certain widow who gave a “mite” — the smallest coin available — in her temple offering, gave all that she had, her utmost; which the Son of God noted and which God his Father would have also. Abundance is overflow but not overmuch.