Why is “and all that is in them” added?

Revelation 5:13 (ESV)

13 And I heard every creature in heaven and on earth and under the earth and in the sea, and all that is in them, saying, “To him who sits on the throne and to the Lamb be blessing and honor and glory and might forever and ever!”

Given how comprehensive the list of participants in this song of praise already was, we might think these additional words are unnecessary. But the Holy Spirit wishes the church of all ages and places to know that there were no exceptions anywhere among those who gave praise to God and to the Lamb. Here is an echo of the closing verse of the final, climatic psalm of the Psalter, Psalm 150:6: “Let everything that has breath praise the Lord!”