Upon graduating from college, marriage, post grad, etc. he would say something to the same effect. Then there were those times like when I entered the military or when our first son was born or when we purchased our first home. My father associated events in life as pages and chapters in the book of one's life. It's a very interesting concept. One could say that we are known by the pages and chapters of our life.
Every day is a sentence or maybe several paragraphs.
In this week's parsha, men within B'nei Yisroel are selected to serve in the army based upon their heritage, upon their family ancestry. The nation as a whole is divided into camps based upon their father's family ancestry. So in this sense we could say that on a larger scale each family member is part of this huge book of history and events, etc. One may think in terms that each of us is a paragraph or a few pages recorded in this massive eternal book. Each of us is inscribed in the Book of Life.