Genesis 2:24
Genesis 2:2424For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh.
JWs cite to establish the Jehovah-ordained pattern for marriage and to ground the Watchtower's teaching on lifelong monogamy and appropriate family roles. The "one flesh" phrase is read descriptively — a union of two distinct persons into one household. No wider theological use is typically made of the verse.
The "one flesh" of is the Hebrew echad — the same word used of Jehovah in ("Jehovah our God is one Jehovah"). Two persons, really distinct, forming one unity. The Jehovah/Adam name analogy draws the parallel at the anthropological level: Adam and Eve share the name "Man" () without Eve being the man Adam; they share one "flesh" () without being one person. The Shema's use of echad — which can mean compound unity, as in 2:24 — is not by itself a Trinity proof, but the pattern of "multiple persons sharing one nature without being identical" is built into creation from day six. Pair with for the name- sharing half of the same picture.