Extraordinary intervention

It seems to me that the point of saying God put Er and Onan to death is to stress that there was an unusual directness about it. God interrupted the more normal processes of life and dying (which he controls) and took them away by a more direct act.

Thus we learn that it is not meaningless to believe that all events are governed by God, and yet to pray that he intervene in extraordinary ways. Governing all does not mean governing all in the same way.

 - John Piper, via the Desiring God blog, emphasis mine

It seems fair to say that God typically responds to the prayers of his saints (broadly, generally speaking) in two ways:

1. Ordinary
2. Extraordinary

I would argue that God ordinarily acts by sustaining creation as it was made ex nihilo 24-7, giving us our daily bread and provision, and the like. We oftentimes see God respond to prayers (or in Er and Onan's case, wickedness) in extraordinary ways. Piper makes a great point in presenting the fact that God is sovereign over absolutely everything in the universe right alongside the fact that it is meaningful to pray/expect that God in extraordinary ways.

Let all the extraordinary acts of God recorded for us be motivation to ask God to move in such ways, for his glory.