For someone interested in Kepler this is an interesting book, although the emphasis is more on Tübingen and theology than on Kepler and mathematics.
The human mind is created to do mathematics. According to Melanchthon, the atomistic doctrines of creation by chance "wage war against human nature, which was clearly founded to understand divine things" (p. 76); astronomical observations are as natural to a human being as "swimming to a fish or singing to a nightingale" (p. 85). Kepler elaborates: "Rather, as we do not ask what hope or gain makes a little bird warble, since we know that it takes delight in singing because it is for that very singing that a bird was made, so there is no need to ask why the human mind undertakes such toil in seeking out these secrets of the heavens" (p. 207).
The purpose of scientific study is therefore twofold. (1) "inflaming their souls with love and enthusiasm for the truth and rousing them to understanding of the noblest things" (Melanchthon, p. 73). "[T]he reason why there is such a great variety of things, and treasuries so well concealed in the fabric of the heavens, is so that fresh nourishment should never be lacking for the human mind, and it ... should have in this universe an inexhaustible workshop in which to busy itself" (Kepler, p. 208). (2) Astronomers are "priests of the book of nature" (Kepler, p. 206n3). The existence of God follows from the universe's "beauty, order, and all things which have been founded for settled purposes" (Heerbrand, p. 137). "God desired that knowledge of the wonderful courses and powers should lead us towards knowledge of the divine" (Melanchthon, p. 76).
Another influence is of course Maestlin who proved by parallax that the 1572 nova was a star (p. 173) and that comets are "in the height of the aether" (p. 179).
"Where is Platonism? Where, for that matter, is Neoplatonism, or the Hermetic trends which are to be found in Kepler's thought? They seem not to have been at all current in Tübingen's university circles." (pp. 221-222)