Everything that God has ever said is right. Psalm 66:4 speaks of a future time when all the earth will worship God and sing to Him:
Psalm 66:1 <To the chief Musician, A Song or Psalm.> Make a joyful noise unto God, all ye lands: 2 Sing forth the honour of his name: make his praise glorious. 3 Say unto God, How terrible art thou in thy works! through the greatness of thy power shall thine enemies submit themselves unto thee. 4 All the earth shall worship thee, and shall sing unto thee; they shall sing to thy name. Selah.
All the earth has never yet done so. Whatever God says is going to happen will happen.
Someday, Psalm 66:4 will be fulfilled! All the earth is going to worship God and sing to Him someday!