The song begins with the story of King David who first used the sacred word in his psalms: "Now I've heard there was a secret chord that David played, and it pleased the Lord .... It goes like this: the fourth, the fifth, the minor fall, the major lift, the baffled king composing Hallelujah."
Scientists tell us there is background radiation that permeates the universe, white noise emanating from the Big Bang, the moment of creation. It can be heard as static on radios and televisions when no earthly signal gets in the way.
The Hindus say this sound is the sacred syllable AUM (also spelled Om). Lao Tzu, the philosopher of ancient China, called it Tao. The Greek philosophers called it Logos, meaning Word, the basic principle of the universe. The apostle John opened his Gospel with this same Greek word and says that the Word was incarnated in Jesus.
I have heard the chord, and I suspect that you have also. The psalmist said that the heavens sing it day and night. Not with words, but with an audible silence that goes to the ends of the cosmos. "Their words aren't heard, their voices aren't recorded, But their silence fills the earth: unspoken truth is spoken everywhere." (Psalm 19:3-4) The apostle Paul described it as "words taught by the Spirit, expressing spiritual truths in spiritual words." (I Corinthians 2:13)
I hear it when my heart is quiet enough to pay attention to the Song beneath the noisy ramblings of my mind. But it is not AUM or Tao I hear. I hear Hallelujah! Handel recorded it in his Hallelujah Chorus. The apostle John wrote the words to the song in Revelation 19:1-4.
The version of Hallelujah that k.d.lang sang does not have the original lyrics. She chose to sing a later version. (It went through four revisions from 1984 to 2008. You can read the account of the revisions here.) The last verse was changed from words of faith and praise to words of doubt and violence. She sang, "Well maybe there's a god above. But all I've ever learned from love was how to shoot somebody who'd out drew ya.... It's a cold and broken Hallelujah."
I cannot imagine why anyone would change a song of worship to one of despair, but I guess the darkness of the human heart should no longer surprise me. The closing words of the song, as originally written by composer Leonard Cohen, are these: "I'll stand before the Lord of Song with nothing on my tongue but Hallelujah!" To that I can only say "Amen! Hallelujah!"