be to do something

formal

1) used for telling someone what to do

You are to stay here until I send for you.

2) used for saying what has been arranged

The ceremony is to take place in the palace grounds.

3) used for saying or asking what should be done

What are we to do?

You are to be congratulated on your wise decision.

4) used in an "if" clause for suggesting a possible aim when you are saying what must happen in order to achieve it

If we are to compete successfully in world markets, we must invest more money in education and training.

5) used about someone or something in the past to say what would happen at a later time

the boy who was to become king