Rob has series of posts on baptism, which is over all interesting. This point in particular, however, is one which must be drawn and then explained by those who hold to the same view point as Zwingli:
The view that baptism relates primarily to justification and essential for the forgiveness of sins was the predominate view that continued far past the early Patristics continued until the Reformers (I’ve researched many hours and I’m yet to find an opposing viewpoint before Zwingli, but I surely welcome corrective data if its out there). With the implications of the Reformation period in mind, however, it makes logical sense that such a shift of focus would occur since this period began thinking of salvation by faith alone.
How is it that only Zwingli, 1500 or so years removed from the Apostles, suddenly understood baptism?
For more information, check out this article.