Rhetorical: Zeezrom has asked for information, and Alma's first statement is that the Lord tells some people, but that the Lord also constrains some information. Why does Alma begin this way, and then start explaining things? Alma is answering the implicit question that Zeezrom is asking, not the explicit one. While Zeezrom has opening asked for more information, it would appear that Alma's perception of his heart sees another unstated question, which is "why don't I know about this?" Zeezrom was a lawyer, and well educated man. He expected that he had received an education sufficient in the most important things, and he has now found that background wanting. Why didn't he know this?
Alma tells him that there are things that the Lord can only reveal to those whose hearts are ready for them. Zeezrom and his fellow lawyers, those who have created the acceptance of the order of the Nehors, were not in a position to want to hear. However, now Zeezrom's heart has been opened, and therefore Alma can answer his question.