Matthew 13:33
Matthew 13:3333He told them still another parable: “The kingdom of heaven is like leaven that a woman took and mixed into three measures of flour, until all of it was leavened.”
The Watchtower applies the leaven parable to the spread of Jehovah's organisation worldwide — the "kingdom message" being worked through the global Witness preaching network. The expansion is read as evidence of Jehovah's blessing on his earthly organisation, with the eight-million-plus publishers as the visible measure of the leavening process. The parable's trajectory is mapped onto Watchtower growth specifically.
The leaven parable is about the Kingdom of God, not about any named denomination. Jesus says "the Kingdom of the heavens is like" leaven — not "the Watchtower" or any other organisation. The Kingdom has grown massively over two thousand years from twelve apostles to several billion professing Christians. Pair with (the stone becoming a mountain that fills the earth), (the mustard seed parable), and ("the Kingdom of God is in your midst"). The Kingdom's growth is global, ongoing, and trans-denominational. It is fulfilled in the worldwide movement of those who profess Christ — Reformed, Catholic, Orthodox, African, Asian, the underground Chinese church — not in a branch claiming exclusive identity with the leaven.