Why did Galileo address this letter to his student, in response to the earlier correspondence, who was already a supporter of Galileo’s views and the Copernican theory?

Answer one of the following questions:
1) Why did Galileo address this letter to his student, in response to the earlier correspondence, who was already a supporter of Galileo’s views and the Copernican theory? Why would he not address the other side of the argument, the political parties who attempted to disprove his views?

2)Why did Galileo not make these arguments directly to those people that argued his theory with Benedetto Castelli? Why waste his time advising Benedetto how to better argue the Copernicus theory, instead of arguing it himself, with his own, far more knowledgeable beliefs?

3)How was the Copernicus Theory invented without any new information or evidence? What made Galileo such a faithful believer before proof was researched and provided as to such?