The abandoned diary

Ergo,
It is a fancy way to say 'Therefore' or simply 'so'. However, this author, as you know, loves something platonic and flowery.
Those three words are usually used to start a conclusion, (They serve their function as linking words). Thus, this book presumably can be taken as a public diary where all the conclusions in the author's mind are put into words.
Ergo,
I open for you to the door of my mind.