Psalms - Chapter 100
Ivdu Es Hashem B'Simcha
The fourth "book" of Psalms began with Psalm 90 and the first eleven Psalms are attributed to Moses. This is the final Psalm in that series.
A song of thanks: let the whole world call out to G-d and serve Him happily, coming before Him singing joyfully. Recognize that Hashem is the only G-d, Who made us. We are his, like sheep in His field. Approach the Temple with increasing joy - thanks in the gates and praise in the courtyards. Bless G-d because He is all good. His kindness lasts forever and He can be relied upon from generation to generation.
Psalm 100 is recited most weekdays during the morning service and it is the source of the familiar song "Ivdu Es Hashem B'Simcha" ("Serve Hashem with Joy").