What is the purpose of friar laurence soliloquy at the beginning of the section

In Act 2, scene 3 from "Romeo and Juliet," by William Shakespeare, Friar Lawrence's soliloquy makes reference to the healing effectiveness of herbs and medicinal plants, at the same time they can be poisonous. As a consequence, he suggests that good qualities in nature and in people can lead to destruction if not used in the exact manner. Thus, he foreshadows the tragic death of the lovers.