Psalms 94:1

קל נְקָמוֹת ה’ קל נְקָמוֹת הוֹפִיעַ

G-d of vengeance, Hashem! G-d of vengeance, shine forth!

This is the Psalm of the Day for Wednesday, which is the fourth day of the week. The Talmud in Rosh Hashana (31a) explains the connection between this Psalm and Wednesday. This Psalm refers to Hashem as a “G-d of vengeance.” On the Wednesday of Creation, G-d created the sun and the moon. These were later worshipped by idolaters, from whom G-d will extract vengeance.