1. One possible positive consequence of Japanese isolation that Hall points out is that it ensured peace for the country, and allowed it to develop its political and economic institutions without foreign influence, which was a large problem at the time for developing countries. Foreign influence often inhibited development of developing countries, so closure prevented this.
2. The main fear which caused the shogun to close Japan to the West was the growing influence of Christianity, and the effect it would have on Japan's political world. Christianity is predominantly a Western religion, and having that sort of Western influence upon a developing country could have detrimental effects on the country, like political division.
3. Spain's activities in the Philippines served as a warning to the Japanese by showing them that by sending missionaries to a country and converting the populous, you could essentially take over the country. This inclined the Japanese government to institute new policies that would prevent missionary activity in the country, by forbidding Spain, as well as Portugal, from visiting the country.
