"the whole life and substance of the Church is in the Word of God"

"The gospel is, before bread and Baptism, the sole most certain and most noble mark [(symbolum)] of the Church, since [it is] by the gospel alone [that] it is conceived, formed, fed, produced, educated, led out to pasture, clothed, adorned, fortified, armed, conserved; in a word, the whole life and substance of the Church is in the Word of God, as Christ says:  'Man lives by every word that proceeds from the mouth of God.'"

"Euangelium enim prae pane et Baptismo unicum, certissimum et nobilissimum Ecclesiae symbolum est, cum per solum Euangelium concipiatur, formetur, alatur, generetur, educetur, pascatur, vestiatur, ornetur, roberetur, armetur, servetur, breviter, tota vita et substantia Ecclesiae est in verbo dei, sicut Christus dicit 'In omni verbo quod procedit de ore dei vivit homo.'"

     Martin Luther, Ad librum eximii magistri nostri Mag. Ambrosii Catharini, defensoris Silv. Prieratis acerrimi, responsio (1521), WA 7, 721 (705-778), ll. 9-14, quick-and-dirty translation mine.  I have not read around in this treatise, which has not yet (?) appeared in English, but is no. 1.42 on the Prospectus for the supplement to Luther's works.