God's words are always true. When God swears by his own name, it shows he will never break his promise (see also Isaiah 14:24; 54:9; 62:8; Hebrews 6:13).
Every knee … every tongue: At the end of time, all nations will accept his authority, either willingly or unwillingly (see Romans 14:11; 1 Corinthians 15:25–27; Philippians 2:10–11).