He could have chosen to speak directly from heaven to people on earth. Jesus said that Jehovah could even have had the stones cry out about the Messianic King.
بِٱلطَّبْعِ ،‏ لَيْسَ يَهْوَهُ مُضْطَرًّا أَنْ يُشْرِكَنَا فِي هٰذَا ٱلْعَمَلِ .‏