As usual, Bilaam speaks out of both sides of his mouth. On the one hand, he seeks to excuse himself for his actions, claiming, Lo yadati, “I did not know” that you (the angel) stood before me. On the other hand, he concedes, Chatasi, “I sinned.” What is it: excuse, or sin? He cannot have it both ways. The Shlah HaKadosh explains that the two go together – chatasi, ki lo yadaati, “I sinned, because I did not know.” The mere fact that I did not know is a sin.
How can Bilaam claim that he was unaware, that he did not know? He himself said that his donkey was perfect; it had never before acted with such insolence! (His donkey was well-behaved; it had never given him any trouble.) This alone should have been to Bilaam (who was a pagan prophet) a sign from Hashem. Hashem was speaking to him. He should have immediately asked himself, “What does G-d want from me?”
Instead, he closed his eyes; he ignored the signs. This, in and of itself is a sin. When one chooses to ignore a message from G-d, claiming that he did not notice it, he is guilty of a spiritual deficiency. Let me add, that when one purposely closes his eyes and refuses to see the message vividly presented to him, he goes beyond ignorance- to the point of utter brainlessness.
There are times, observes Horav Reuven Karlinstein, zl, when a person is sent a message from Heaven, such as an illness accompanied with such extreme pain that one must be blind not to see that Hashem is speaking to him. The Almighty wants him to wake up, look around, think, introspect. Yet, he chooses to ignore the message. Why? It is too much to handle. He would rather experience the pain than change his ways. So, he simply closes his eyes. Ignorance may be bliss, but, at one point, it becomes obtuseness.
Ignorance as a sin is different from the legal jargon, Ignorantia juris non excusat, which means that people cannot claim ignorance of the law as an excuse for absolving an illegal act. Ignorance as a sin means that we are responsible for our lack of knowledge. We should have known; we should have listened; we should have opened up our eyes and seen the message. One who “should have,” but did not, is a sinner. It is as simple as that.