Blaise Pascal (1623-1662) toiled on a master work most of his life, a massive opus reconciling philosophy, mathematics, Catholicism, faith, reason, and even rhetoric. He failed. The book(s) never materialized, but a collection of notes toward the book(s) survived. It's now called Pensées.
It's one of those books one may read in, as opposed to reading, and every return-trip is as pleasurable as an earlier one. A good history of philosophy functions similarly, as does a book of aphorisms or Fowler's book on usage in English. Dag Hammarskjold's Markings is similar in form to Pensées, but Hammarskjold intended to write an interior, private, meditative diary, so he produced the book he had intended to produce (but not to publish, at least in his lifetime), whereas Pensées is an and accidental classic, its complete unevenness part of its charm. Pascal died thinking he had nothing more than a collection of notes. He was right. And wrong. His interminable warm-up to the book ended up being the book, and some of the entries are so pithy as to be poetic.
So you might find something lofty like this (quotations take from the Oxford World Classics paperback edition translated by Honor Levi):
#225 "Knowing God without knowing our wretchedness leads to pride. Knowing our wretchedness without knowing God leads to despair. Knowing Jesus Christ is the middle course, because in him we find both God and our wretchedness." (p. 65)
But then you might run into a stray line that truly is just a note to himself: "I too will have thoughts at the back of my mind." Nothing leads up to this, and nothing follows it, so you just have to think, "Thanks for that, Blaise."
A few favorites of mine:
"Power is the mistress of the world, not opinion. But it is opinion which exploits power." (p. 115)
"Languages are ciphers in which letters are not changed into letters, but words into words. So an unknown language is decipherable." (p. 115) This is no longer a profound observation, of course, but it still says much succinctly about language-acquisition, translation, and cryptology.
"When wickedness has reason on its side, it becomes proud, and shows off reason in all its lustre." (p. 113).
#213 "There is nothing so consistent with reason as the denial of reason." (p. 62).
#214 "Two excesses. Excluding reason, allowing only reason. (p. 62).
Then there's the famous "wager," a section of the book in which Pascal argues that if you are forced to wager whether whether God exists, you should bet that God does exist because if you bet that God doesn't exist and lose, then your soul might be in danger, whereas if you bet that God does exist and you lose, you haven't lost anything.
One more I like:
(p. 149): "The more intelligent we are, the more readily we recognize individual personality in others. The crowd finds no difference between people."
The book also includes a stand-alone treatise on rhetoric that holds up pretty well.
Different people will find different morsels to enjoy from this French philosophical, religious, meditative, aphoristic buffet of Pascal's. If you can locate a copy, just start flipping through it, and something will catch your eye, intrigue your reason, your personality, your obsessions, and/or your curiosity. It's a book that goes nowhere and everywhere.