Romeo and juliet- at the beginning of act 2, scene 3, why does friar lawrence spend so much time discussing his passion for herbs and alchemy?

In the scene, Friar Lawrence meditates on the duality of good and evil that exists in all things. Speaking of medicinal plants, the friar claims that even though everything in nature has a purpose, it can also lead to misfortune if used improperly. 

Ido have a poem that i wrote in my english class if you would like it.