Why I haven't read The Pilgrim's Progress

Justin Taylor recently expressed worry for the future readership of John Bunyan's allegorical classic, The Pilgrim's Progress. I found it a bit ironic, having tried to read The Pilgrim's Progress twice and failing both times. As with most books I don't finish, this isn't because I lost interest but because I encountered something I disliked enough to stop reading. In both cases, it was this passage:

Now, said Christian, let me go hence. Nay, stay, said the Interpreter, till I have shewed thee a little more, and after that thou shalt go on thy way. So he took him by the hand again, and led him into a very dark room, where there sat a man in an iron cage.
Now the man, to look on, seemed very sad; he sat with his eyes looking down to the ground, his hands folded together, and he sighed as if he would break his heart. Then said Christian, What means this? At which the Interpreter bid him talk with the man.
Then said Christian to the man, What art thou? The man answered, I am what I was not once.
CHRISTIAN: What wast thou once?
MAN: The man said, I was once a fair and flourishing professor, both in mine own eyes, and also in the eyes of others; I once was, as I thought, fair for the Celestial City, and had then even joy at the thoughts that I should get thither. [Luke 8:13]
CHRISTIAN: Well, but what art thou now?
MAN: I am now a man of despair, and am shut up in it, as in this iron cage. I cannot get out. Oh, now I cannot!
CHRISTIAN: But how camest thou in this condition?
MAN: I left off to watch and be sober. I laid the reins, upon the neck of my lusts; I sinned against the light of the Word and the goodness of God; I have grieved the Spirit, and he is gone; I tempted the devil, and he is come to me; I have provoked God to anger, and he has left me: I have so hardened my heart, that I cannot repent.
Then said Christian to the Interpreter, But is there no hope for such a man as this? Ask him, said the Interpreter. Nay, said Christian, pray, Sir, do you.
INTERPRETER: Then said the Interpreter, Is there no hope, but you must be kept in the iron cage of despair?
MAN: No, none at all.
INTERPRETER: Why, the Son of the Blessed is very pitiful.
MAN: I have crucified him to myself afresh [Heb. 6:6]; I have despised his person [Luke 19:14]; I have despised his righteousness; I have "counted his blood an unholy thing"; I have "done despite to the Spirit of grace". [Heb. 10:28-29] Therefore I have shut myself out of all the promises, and there now remains to me nothing but threatenings, dreadful threatenings, fearful threatenings, of certain judgement and fiery indignation, which shall devour me as an adversary.
INTERPRETER: For what did you bring yourself into this condition?
MAN: For the lusts, pleasures, and profits of this world; in the enjoyment of which I did then promise myself much delight; but now every one of those things also bite me, and gnaw me like a burning worm.
INTERPRETER: But canst thou not now repent and turn?
MAN: God hath denied me repentance. His Word gives me no encouragement to believe; yea, himself hath shut me up in this iron cage; nor can all the men in the world let me out. O eternity, eternity! how shall I grapple with the misery that I must meet with in eternity!
INTERPRETER: Then said the Interpreter to Christian, Let this man's misery be remembered by thee, and be an everlasting caution to thee.
CHRISTIAN: Well, said Christian, this is fearful! God help me to watch and be sober, and to pray that I may shun the cause of this man's misery! Sir, is it not time for me to go on my way now?
INTERPRETER: Tarry till I shall show thee one thing more, and then thou shalt go on thy way.

"God hath denied me repentance." It baffles me how this book can be considered such a spiritual classic when contains this expression of a message so antithetical to the gospel. Even if Bunyan were talking about the "unforgivable sin" (which he makes no attempt to do), I would dispute his theology. God's grace and patience have no limits. We can't wear Him down until he decides with one more sin, "You're done" and shuts us out of His presence, denying us grace no matter how much we may plead and repent. God is better than that, no matter how bad we are.

More directly: the whole, entire story of Scripture is about God recklessly pursuing sinful people even as they reject and sin against Him. This prodigal grace doesn't stop or get replaced by the expectation of keeping your nose clean once we become Christians. God will never shut us out, we can only shut Him out. However we interpret the solemn warnings in Hebrews 6 and 10 which Bunyan references, we must read them in a way worthy of God. I simply can't say that The Pilgrim's Progress does.