Rashi: All that you saw in the Mazalos will be covered from you like a letter sealed with wax. "They give it to one who knows how to read, and he says 'I cannot

Rashi: It is a letter sealed with wax.

Radak: Its words are covered and sealed.

Rashi: He cannot see inside, since it is sealed.

Radak: He makes this excuse because he does not want to read it. If he wanted, he would open it and read it! So the Chachamim among you say that there are hidden things in Hashem's words, therefore they do not heed them. If they wanted to hear and understand, they would tell the Navi 'explain to us this hidden matter!'

Malbim: Because you thought that just like your eyes are covered from seeing, also the Nevi'im's eyes do not see, the prophecy of all Nevi'im is to you like a sealed book. You think that even though the Navi knows his mission, he does not know the explanation of his words, for Hashem sealed the Sefer and letter and gave it to him to bring to the nation. Even the Navi may not open it. You think that if you will ask him to read it, he will say that he cannot, for he may not open it.