Interpretation of Siddhartha by Herman Hesse
The paper titled "Between reverence and revolt:
Hesse and the two faces of religion" suggests that Hesse was primarily a (Christian) Protestant.

It says for example that in his 1921 diary he wrote:


  “And now the whole of Buddhism increasingly appears to me to be
  a kind of Indian Reformation, an exact equivalent of the Christian one”


So far as I know, a primary Protestant belief is that people are saved by God (maybe by their love of God and/or by God's love): a Christian's duty (to God) is faith and obediance, which God rewards with salvation (perhaps miraculous salvation).

I think it's also (especially in contrast with pre-Reformation Catholicism) something to do with a personal relationship, unmediated by clergy (and perhaps by ritual), between each person and God.

I guess that influences this sentence:


   But while Govinda with astonishment, and yet drawn by great love and expectation, obeyed his words, bent down closely to him and touched his forehead with his lips, something miraculous happened to him.


You wrote, " It's always been completely mysterious to me." Perhaps that's because it's so Christian-influenced.