"The difference between Christianity and the Gnostic spirit"

"A sign that belongs to a proper language, constituted by knowable semantic and syntactic rules, can be replaced in the language by some other sound or mark, following the same semantic rules by which the sign was specified in the first place.  But we are not in a position to do this with such signs as the bath of baptism.  We are not able to create a different ceremony of initiation—say, the giving of a particular lifelong haircut—and declare that this will now mean what baptism has meant.  The reason is that we possess no semantic rules to control the translation.
  "The Supper's loaf and baptism's bath cannot be replaced because we cannot know the rules by which they were 'instituted'—that is, given force as signs.  We can know that they are signs, and even take them as signs into our discourse, with its rules.  Indeed, we can even after the fact sometimes work out how these signs are apt to their purpose—why, for example, bread and cup are apt to mean the crucified Messiah.  But we do not know the rules of these signs' home language; we do not know why God says 'I am with you' by bread and cup instead of by some other signs.  For us, the givenness of the loaf and the bath can be nothing but historical contingencies to which we are bound as we are bound to the contingencies of God's choice of Israel from the nations or of Mary from the maidens of Israel or of Jesus from Mary's many possible children.  Accordingly, we are not able to translate cup and bath into true equivalents; the res themselves are inseparable from their meaning.
  "The language by whose rules bread and cup and bath are instituted can only be the language of God and his saints.  It is the language of a community to which we now belong only across the line of death and new creation; our possession now of some of its signs is mysterious in the strict sense.  For it is identical with the identity across death and resurrection of the sinner that I was with the saint that I will be. . . .
  "The saints in heaven may know God so well as to make new names for him to suit their love; perhaps they do it instant by instant.  But we have membership in their company only across death and resurrection.  How do we know any names for God?  Or that 'The Father begets the Son' is a meaningful and true sentence?  Only if he lets us overhear, across the border of our own non-being and new being, the conversations of heaven. . . . And why he and his saints let us overhear one name instead of another, one phrase instead of another, we do not know at all. . . .
". . . The difference between Christianity and the Gnostic spirit is then simple and straightforward:  for the latter, apophaticism means that we have continuously to make up language in which to speak of God, since all speech fails as soon as it is used; for Christianity, apophaticism means that we are given language that is immune to our manipulating, that is 'sacramental' in its destiny."

  Robert W. Jenson, "'The Father, He . . .'", in Speaking the Christian God: the Holy Trinity and the challenge of feminism, ed. Alvin F. Kimel (Grand Rapids, MI:  Eerdmans, 1992), 107-109.