Pentecost began as a Jewish celebration of the wheat harvest in the late spring. No specific date was set it took place when the harvest was ready.
Gradually it became customary to celebrate the feast 50 days after the Passover. This gave it additional meaning. Jewish scholars had calculated that when their ancestors left Egypt, they arrived at Mount Sinai approximately 50 days later. It was there that God gave the Law and made a Covenant with them: I will be your God, and you will be my people.
Thus, Pentecost became a time to celebrate the covenant that made them Gods chosen people.
Lukes description of the Spirit coming upon the disciples on the very day of this Jewish feast emphasizes the understanding of Christianity as a new covenant.
The word Pentecost is Greek for 50th day.
Jesus uses a homey parable to help his disciples understand that his departure will ultimately bring them joy.
We can use that parable to help us face the dying we have to go through in life.
Dying is a law of life. To go to another level we have to die to the level we are at. The infant has to give way (die) to infancy in order to become (be born) the child. The child has to die to childhood to become the teenager. And on it goes the teenager has to become the adult and the adult has to become the old person and the old person has to die to be born into the fullness of life.
There is continuity (we are the same person before and after) but also discontinuity (we have to let go of the previous life).
Did God set things up this way just to make it difficult? No.
If we are to be free human beings (not robots or animals acting on instinct) destined to become god-like it could be no other way. Think about it. Talk it over with the Lord.