John Calvin Commentary Isaiah 10:19

"And the remnant of the trees of his forest shall be few, so that a child may write them." — Isaiah 10:19 (ASV)

And the remnant of the trees of his forest shall be a number. When he adds that the remnant of them will be a number, he employs a Hebrew idiom to express that they will be few. Thus, he only confirms the former statement: the devastation produced after the calamity which God will bring on the Assyrians will be so great that there will be no difficulty in counting them.

That a child may number them. He goes so far as to say that they will be so few that those who are left of them may be counted even by a child. For children have difficulty counting as far as three or four. Accordingly, the kingdom of the Assyrians was formerly like some vast forest; but when the trees have been hewn and thrown down, those which are left are few, and scattered at great distances from each other.