The writer of this letter appears to be confused. He addresses the philosophical question, What is life? while ignoring the observable fact that a particular life can be traced back to the moment of conception, and no further.
Put another way, the distinction between life and non-life involves one set of philosophical questions, whereas the identification of the moment a certain life begins involves a different set of questions.
Biologists consider eggs and sperm to be living things, as is the earliest product of fertilization. However, it is when fertilization occurs that the development of a new individual organism begins.
Contrary to the LTE, that is the significance of the moment conception.