I always thought he was INFJ. Here are some quotes from his book that made me think so:
"What matters, therefore, is not the meaning of life in general, but rather the specific meaning of a person's life at a given moment."
"A man who becomes conscious of the responsibility he bears toward a human being who affectionately waits for him, or to an unfinished work, will never be able to throw away his life. He knows the "why" for his existence, and will be able to bear almost any "how."
"It did not really matter what we expected from life, but rather what life expected from us. We needed to stop asking about the meaning of life, and instead to think of ourselves as those who were being questioned by life - daily and hourly. Our answer must consist, not in talk and meditation, but in right action and in right conduct. Life ultimately means taking the responsibility to find the right answer to its problems and to fulfill the tasks which it constantly sets for each individual."
"I grasped the meaning of the greatest secret that human poetry and human thought and belief have to impart: The salvation of man is through love and in love."
Also, he seems to have flashes of insights in his story and uses signs as a way to make sense of things. At one point, he talks about trying to decide to stay with his family, or move away to study his profession. He notices one of the ten commandments, that says "Honor thy mother and father", at one point, and decides to remain with them. This seems INFJ to me. Do you think it could be INFP though too?