Whatever his reasons, God didn’t choose the biblical patriarchs for their virtue. Lot cavorted with his own daughters.Jacob tricked his blind old father into bestowing on him the blessing meant for his brother; he’d already bribed Esau out of his birthright. The matriarchs weren’t any better: Jacob’s mother Rachel put him up to the scam. Jacob himself was later cheated by his father-in-law Laban. Rachel and Leah, the two wives whom he toiled for 14 years to win, competed bitterly, each conniving to trump the other in offspring. Jacob’s sons (with the exception of Joseph) were even worse. When his jealous brothers decided to kill Joseph, Reuben, the eldest, was concerned only that they wouldn’t realize enough profit from the crime. The same Reuben slept with his father’s concubine Bilhah, thus defiling Jacob’s bed. The list goes on. And yet, these same men and women, with their lusts and rages, stood in the presence of God and spoke with him, wrestled with angels and saw celestial ladders rising to heaven.

The puzzle isn’t why God chose such flawed vessels but why the Bible so scrupulously recorded their misdeeds. Most of these are related in Genesis (though Moses too has his moments in the later books),and that raised a vexing problem for pious commentators, Christian as well as Jewish. Why was Genesis included in the Torah, and why was it placed first in order? Even Rashi, the greatest biblical commentator, raised the question as late as the 11th century. Genesis contains no revealed law; and it wasn’t really credible that such figures as Reuben or even Jacob — let alone the bibulous Lot or the slow-witted Esau — were meant to serve as models of behavior. From a contemporary perspective, we might say it’s part of the glory of the Hebrew scripture that it blinks at nothing. But for devout believers from the earliest period the only recourse was either to explain instances of wickedness away or to claim that it somehow served the inscrutable divine plan. In any case, this was but one of the swarming textual difficulties that confronted these earnest readers.

In his elegant new book,”The Ladder of Jacob: Ancient Interpretations of the Biblical Story of Jacob and His Children” (Princeton; 280 pages; $24.95), James L. Kugel takes on these, and even more perplexing, questions with great erudition and admirable lucidity. Mr. Kugel is Professor of Bible at Bar-Ilan University and a world authority on the history of the biblical texts and their interpretation. Whether unravelling some philological tangle or reconciling divergent readings, he has the enviable knack of capturing his reader’s attention and keeping it firmly tethered. He draws on sources in Hebrew and Aramaic, Greek and Latin, with forays into Syriac and Old Slavonic, but the effect is seldom pedantic.This is a scholarly work but not, in the end, an academic one; the riddles that tantalized the early commentators, however abstruse they may at first seem, vex us still.

This is Mr. Kugel’s 10th book on scriptural hermeneutics and perhaps his most fascinating; for here he takes on the appalling family of Jacob in all its mingled squalor and grandeur. As he puts it, “‘Dysfunctional’ is probably the first word an observer would use to describe such a family in modern times.” That seems an understatement. And yet, the five episodes he considers touch on virtually every aspect of the human predicament.

One interesting result of his approach is that we steadily see how differently earlier readers interpreted a text. Genesis 28 contains the famous dream-vision that Jacob had on the way to Haran: “He had a dream; a ladder was stuck into the ground and its top reached up to heaven, and the angels of God were going up and down on it. And the Lord was standing over him and He said, ‘I am the Lord, the God of Abraham your father and the God of Isaac; the land upon which you are lying I am giving to you and your descendants.” This passage had never struck me as problematic. But it bothered ancient readers. What was the point of the ladder? Couldn’t God have spoken directly to Jacob? And why, after he heard the voice of the Lord, did Jacob grow frightened and say, “How fearsome is this place!” Wasn’t God’s message with its promise of covenant reassuring?

The ladder itself called forth highly creative speculation. For Philo it represented the “ups and downs” of human experience. Others were intrigued by the statement that the angels were “going up and down” on it. If they were going up, they must have begun from the ground. What were the angels doing on the ground in the first place? Some suggested that they had been on a previous mission; but if so, why had they stayed so long before ascending again? One puzzle bred others. The text was a mere seed, the commentaries that sprouted from it a vast bramble that somehow, over centuries, came to cohere.

Certain episodes had an intense moral dimension. In Genesis 34, Jacob’s only daughter, Dinah, is raped by Shechem, the son of Hamor the Hivite. Shechem falls in love with Dinah and wants to marry her but her brothers are enraged; they demand that the men of Shechem be circumcised before any wedding. The men comply; three days later, Simeon and Levi put them to the sword and destroy the city. Was the demand for circumcision a mere ruse and so, a lie? Why did all the men of Shechem have to die for the crime of one of them? The retribution seems worse than the offense.

Whether discussing Reuben’s sin with Bilhah or the priesthood of Levi or Judah and Tamar, Mr. Kugel moves easily from moral dilemmas to textual enigmas; his book thus serves as a guide to interpretation as well. He analyzes motifs and explains such hermeneutic devices as “notariqon,” a method for explaining ambiguous words by breaking them down into their hidden components (as if we would gloss the word “hearth” by saying that it was composed of “heart” and “earth”). As he notes, exegesis itself became a kind of Jacob’s ladder over the centuries, with rungs capable of spanning the lowest and the highest in one swoop. His own book has that laddered quality. Maybe the point isn’t to reach the top of the ladder but to keep that angelic procession going up and going down to the end of time.