What is the purpose of semicolons? Why not come to a complete stop and put a period? Or are there other uses that I don't know about?
They signal a major shift of tone mid-sentence.
The wonderful Lynn Truss (author of Eats, Shoots and Leaves ) likened the period/full stop to a whole note in music, the colon to a 3/4 note. the semicolon to a half note and the comma to a quarter note. Each suggests a different length of pause, but each also serves a slightly different function.
A sentence is a group of words containing a complete thought. The period ends the thought and paves the way for a different one. The colon sets us up for a list of items to complete the thought. The semicolon signals a shift of thought or tone without ending the sentence, and the comma gives us a place to breathe.