Philippians 2:10 (ESV)

10 so that at the name of Jesus every knee should bow, in heaven and on earth and under the earth,

The purpose of Jesus’ exaltation is that he be worshipped. Every knee will bow to him. That includes all creatures—wherever they may be—in heaven and on earth and under the earth. This threefold division of the universe is also mentioned in Exodus 20:4 (cf. Ephesians 4:8–10). In Isaiah 45:23 the Lord God of Israel says, To me every knee shall bow. Here this worship concerns Jesus—the name of Jesus (cf. Romans 14:11).