Psalm 117 is the shortest psalm with only two verses. This is really a doxology or praise refrain. All the nations and people are to praise Yahweh for his great steadfast love and enduring faithfulness. This psalm begins and ends with the refrain of “Praise Yahweh,” “alleluia,” the Hebrew “Hallelujah.”
This 4th book of psalms ends with a rousing Alleluia, praise to Yahweh, the Hebrew “Hallelujah.” This doxology praise is an addition to this psalm since it probably belonged at the end of Psalm 105. However, it seems a fitting end to this book of psalms with this everlasting praise to Yahweh with the great “Amen.”
Psalm 100 is like the doxology or ending of the psalms about the kingship of Yahweh. It clearly is a thanksgiving psalm as the title indicates. We are asked to praise Yahweh. Everyone should make a joyful noise as they worship Yahweh with gladness. They are to come into his presence singing.