This part of the exchange seems somewhat anomalous. Zeezrom asked about the resurrection and the final judgment, and rather than answer that question directly, Alma discourses on the fact that some are given to know, and some harden their hearts against what they could know. Alma will, in fact, answer the original question in the next verses, but why this interlude?
Zeezrom is a lawyer and should know the law. He has access to the scriptures and has the learning to understand them, yet he asks a question that Alma declares has already been taught. The unasked question is, therefore, why Zeezrom does not already know these things. To that unasked question, Alma answers that he, and those who have accepted similar ideas about God, have hardened their hearts so that they do not understand the word that has been given.