Question about star wars ESB?

I have a question about The empire strikes back. when luke leaves dagobah after not finishing his training and obi-wan laments to yoda that "he is the last hope", and yoda corrects him by saying there is "another" (which is obviously leia), what purpose does this serve to the overall saga, as leia never became a jedi? wouldnt obi-wan, in actuality, be correct and yoda be mistaken. clarification needed.