“It is good to have Torah with the manner of the land.” “Earth” is called Malchut. The way of Malchut is faith above reason. “It is good to have Torah with the manner of the land” means that if one has a point that he comes to observe the Torah with faith, otherwise he cannot achieve observance of the Torah, meaning to achieve the quality of the Torah, since it is forbidden to teach Torah to idol-worshippers.
Baal HaSulam said that in general, where it says that it is forbidden, it means that it is impossible even though we want to. This comes from the corrections that even though he wants to transgress, he cannot.