How did Luther explain 1 Cor. 7:14?

Luther denied that marriage is a sacrament conferring grace.¹ He said marriage is a “worldly matter” (*weltlich geschefft*).² But 1 Cor. 7:14 says the husband and wife can mutually sanctify one another: >For the unbelieving husband **is sanctified** by the believing wife; and the unbelieving wife **is sanctified** by the believing husband… In view of this verse, how did Luther not think this shows that matrimony confers grace? 1. Reynolds 2016 §17.3 (pp. 742-54)
2. *ibid.* p. 749n102: "*Von Ehesachen* WA 30.3: 205/12–14. *Traubüchlein*, WA 30.3:74/2."