Lundbom argues that the reapeating lines simulate the beating of a hammer and also form a chiasm!

You are my hammer and weapon of war:

a. with you I break nations in pieces;
with you I destroy kingdoms;
b. 21 with you I break in pieces the horse and his rider;
c. with you I break in pieces the chariot and the charioteer;
d. 22 with you I break in pieces man and woman;
e’. with you I break in pieces the old man and the youth;
d’. with you I break in pieces the young man … young    woman;
c’. 23 with you I break in pieces the shepherd and his flock;
b’. with you I break in pieces the farmer and his team;
a’. with you I break in pieces governors and commanders.