“וְיָצָא יְהוָה וְנִלְחַם בַּגּוֹיִם הָהֵם כְּיוֹם הִלָּחֲמוֹ בְּיוֹם קְרָב”
“Then YHVH will go forth and fight against those nations, as when He fights on a day of battle.”
The Zohar quote another event when YHVH went to war against the enemies and asks where is the mercy here.
Then explains that the mercy is expressed in the type of death YHVH brought on the enemies of Israel.
” וְזֹאת תִּהְיֶה הַמַּגֵּפָה אֲשֶׁר יִגֹּף יְהוָה אֶת כָּל הָעַמִּים אֲשֶׁר צָבְאוּ עַל יְרוּשָׁלִָם הָמֵק בְּשָׂרוֹ וְהוּא עֹמֵד עַל רַגְלָיו וְעֵינָיו תִּמַּקְנָה בְחֹרֵיהֶן וּלְשׁוֹנוֹ תִּמַּק בְּפִיהֶם.”
“Now this will be the plague with which YHVH will strike all the peoples who have gone to war against Jerusalem; their flesh will rot while they stand on their feet, and their eyes will rot in their sockets, and their tongue will rot in their mouth.”
The verse describes a terrible image of mass deaths. ‘while they stand on their feet’ means aspect of sudden death that is judgement with mercy. Dying slow with pain is aspect of judgment without mercy because it’s much more difficult.
“יְהוָה כַּגִּבּוֹר יֵצֵא כְּאִישׁ מִלְחָמוֹת יָעִיר קִנְאָה יָרִיעַ אַף יַצְרִיחַ עַל אֹיְבָיו יִתְגַּבָּר”
“YHVH will go forth like a warrior, He will arouse His zeal like a man of war. He will utter a shout, yes, He will raise a war cry. He will prevail against His enemies.”
This verse is one unique place where YHVH appears as judgment without mercy. It describes YHVH as a warrior, meaning that He wears garments of a warrior that represent judgment without mercy.
‘Like a man of war’ is the aspect of a warrior ready with his tools of war and intention to kill.