"You (are / have been) blessed by (the love of God / God's love)" There is no difference between the two in an example like above. This kind of thing would probably only be said by a priest etc though. I would like to say that the phrase "for the love of god" is used in a very different way though, as it indicates being stressed out because of a specific annoying action.

There is no difference. As you keep learning you will see how the writers choose the different phrases to express there own style. Btw "for the love of god" is a common phrase people use when they are very frustrated. Example: Tony's mom sees he still hasnt cleaned his room. Upset, she yells, "for the love of God Tony, I told you to clean your room two hours ago" Be careful when you use this though. This is technically a curse word that has the name of religious figure in it, some people might get really mad id you use it.