Act 2 scene 3 Why is the Friar Lawrence given such a long speech when we first meet him?

In my opinion, Friar Lawrence is given such a long speech
because Shakespeare is foreshadowing what is to come.  You can see this in the content
of the Friar's speech.

The Friar's speech meditates on
herbs and plants and their dual nature.  He points out how they can be used in good ways
and bad ways.

This foreshadows what will happen with Juliet
in particular.  She will drink the potion that the Friar will make out of these
plants.

I think the speech also metaphorically talks about
how something good like love can turn into something bad (the tragedy that is going to
happen).