in heaven and on earth and under the earth: All of creation, including spiritual powers, angels, humans on earth, and those who have died, will one day acknowledge Jesus Christ's authority as Lord (see Ephesians 1:9–10, 21; Colossians 1:20–25; 1 Peter 3:22).
every tongue confess (compare Isaiah 45:23; Romans 14:11): This does not mean everyone will be saved. Not everyone will confess Jesus as Lord willingly out of love and devotion.
Jesus Christ is Lord: God's personal name in the Old Testament, Yahweh, was considered too holy to say aloud. So Jewish people would say Adonai (which means “Lord”) instead. When the Old Testament was translated into Greek, Yahweh was represented by the Greek word kurios (“Lord”). This same title is often used for Jesus in the New Testament.