Thou shalt not destroy — Which is to be understood of a general destruction of them, not of the cutting down some few of them, as the conveniency of the siege might require. Man's life — The sustenance or support of his life.
Related Commentaries of Deuteronomy 20:19
Deuteronomy 20:19
19 When thou shalt besiege a city a long time, in making war against it to take it, thou shalt not destroy the trees thereof by forcing an axe against them: for thou mayest eat of them, and thou shalt not cut them down (for the tree of the field is man's life) to employ them in the siege: