Be + Infinitive, Use
1) to state orders, instructions, requirements etc.
You are to stay here until we call.
2) to state a plan
She is to be married next month.
3) to state an (un)anticipated/(un)expected result
It started as a pleasant, sunny day, but it was to be one of the worst of their lives.
I have read the thread (of MikeNewYork) and can say that indeed two of the sentences from that thread deal with the issue I have brought up in this thread. They are
a. Part of my job as the President's secretary is to help organize conferences and keep him informed.
b. I told him a couple of rumors that I'd heard and his response was to roar with laughter and later tell other friends.
For the sake of focus I am going to eliminate some extra parts which don't add any principal meaning.
a. My job is to help.
b. His response was to roar.
That's all for now. I will give some thinking to it and would be glad to hear some new comments on the issue.