There are two ways in which Google decides to show your page description.
1. Summary which is actually Meta Description of your Hub. It should serve as advertising cope of your page and should be written to entice users to click on the
2. First 160 -165 Characters (including spaces) from content on your page
Depending upon the user query Google search may either show your page summary or what the Search Engine themselves consider relevant to User's search query. What search engine extract they normally pull keywords and phrase surrounding the key words.
It's always wiser to use first 160 words of your posts as summary or meta description of your Hub so as to entice visitors to click on your page