Why are some verses missing in the New World Translation Bible?

Some verses, such as Matthew 18:11; 23:14; Luke 17:36 are missing in the New World Translation used by Jehovah’s Witnesses. However, these verses are ALSO not in the Common Bible (an ecumenical edition for Catholics and Protestants), The New English Bible, and the Catholic Jerusalem Bible, to name a few.

The reason is because these verses actually do not belong in the Bible even though many older translations included them. The original manuscripts of the “New Testament” books (the Christian Greek Scriptures) are not available today for use by translators. No one has discovered a Bible book “autographed,” as it were, by the apostles Paul, John, or others. Yet it is evident that soon after the originals were written, copies began to be made for use by the early Christians. The later copies, those farthest from the originals, tended to have more mistakes.

For more, see
The New World Translation