Only the trees which thou knowest that they be not trees for meat,.... Which might be known not only by their not having fruit upon them, but by other tokens, and even at a time of year when there was no fruit on any, which might be sometimes the season of a siege:thou shalt destroy and cut them down; if so to do was of any disservice to the enemy, or of any service to them, as follows; they had a liberty to destroy them if they would:and thou shall build bulwarks against the city that maketh war, until it be subdued; build bulwarks of the trees cut down, and raise batteries with them, or make machines and engines of the wood of them, to cast stones into the city to annoy the inhabitants of it, in order to make them surrender, and until they do it.
All this may be an emblem of the axe being to be laid to fruitless trees in a moral and spiritual sense; and of trees of righteousness, laden with the fruits of righteousness, the planting of the Lord, being preserved and never to be cut down or rooted up; see Mt 3:10.