Psalms 48:2

גָּדוֹל ה’ וּמְהֻלָּל מְאֹד בְּעִיר אֱלֹקינוּ הַר קָדְשׁוֹ

Great is Hashem and highly to be praised, in the city of our G-d, His holy mountain.

This is the Psalm of the Day for Monday. The Talmud (Rosh Hashana 31a) explains the reason each day was assigned a given Psalm. This verse was selected for Monday – the second day - because it says that G-d is great. On the second day of Creation, G-d separated the Heavens and the Earth, and ruled over them. This is a demonstration of His greatness.