A Fundamental Difference in How Luther and Zwingli Viewed the Word

I've recently started reading This is My Body: Luther's Contention for the Real Presence in the Sacrament of the Altar by Hermann Sasse. He describes a fundamental difference between how Luther and Zwingli saw the relationship between the Holy Spirit and the Word of God:

While Zwingli's view of the Scriptures rests mainly on the doctrine of Augustine, a certain influence of Origen and his allegoric interpretation of the Bible is noticeable.  The clarity of the Bible, however, does not mean that everyone can understand it; the Scriptures are clear and intelligible to the faithful only.  Now, faith comes from the Word of God, but only if and when the Holy Spirit moves the human soul.  Such faith is the true master of a correct understanding of the Divine Word.  Thus, Zwingli, in spite of his Augustinian biblicism, recognizes something as higher than the letter of the Bible.

Here a strong contrast between Luther's and Zwingli's understanding of the Word becomes evident.  For Luther the content of the Word is bound up with the letter.  The Holy Spirit comes to us in the external word.  In Zwingli's opinion, the external word (the letter) in itself has no power over the human soul.

Not the content of the Word as such overpowers the soul by virtue of the Spirit that dwells in the Word, but the Spirit contacts the soul directly and thus enables the soul to understand the real meaning of the Word –

So Reinhold Seeberg puts it, and underlines the parallel existing between the understanding of the Word and the Sacrament.  According to Luther, the meaning of the sacramental words can be found in those words only, since they are the words of Christ and, therefore, words in which the Holy Spirit dwells.  For Zwingli they cannot be understood from the letter, but by the Spirit, who makes the believer understand the words when he compares Scripture with Scripture and asks for the analogy of faith (pp. 116, Revised Edition, emphasis mine).

So for Luther, God's words themselves convey the Holy Spirit, but for Zwingli, the Word may or may not be accompanied by the Spirit.  Not only does this work itself out in their radically different views on the Lord's Supper, but it seems also to have very serious implications for their respective theological descendants. This is an issue of certainty – how do I know the Holy Spirit is working in my life?

For Luther it was a no-brainer – the Holy Spirit is always accompanied by the Word, and the Word is never unaccompanied by the Holy Spirit.  The two are inseparable.  For Luther Baptism was efficacious because of the Word of God in and with the water, and where the Word of God is, there is the Holy Spirit.  We receive the true body and blood of Christ in the Lord's Supper because of the Words of Christ.  The Word of God creates what it says.  It is living and active because it is always accompanied by the Spirit.  The person him/herself may reject that Word, but the Spirit is always present in it.

For Zwingli and Calvin et al, however, this is not necessarily the case. One might hear the Word of God, but the Holy Spirit may or may not accompany it.  The Spirit is not necessarily in the Word, but works directly upon a person's heart.  So we cannot really know with certainty that the Holy Spirit is working when one hears the Word, is baptized, or receives the Lord's Supper. 

This is basically where non-Lutheran Protestantism finds itself.  The problem with this is the resulting subjectivity.  I can hear the Word being preached.  I can see a person being baptized.  I can taste the bread and the wine in the Lord's Supper.  I cannot see the Holy Spirit working directly on a person's heart.  

As a Lutheran, I know the Holy Spirit is working because the Word is being preached and the Sacraments are being administered according to Christ's command.  If the Holy Spirit is separated from the Word of God, how can one know with certainty the Holy Spirit is working?  Only through subjective, inward-looking means.  This is true whether one is Calvinist or Arminian.  It is true whether one is Pentecostal, evangelical or fundamentalist.  The precise nature of the navel-gazing may differ from group to group but it is still navel-gazing.