The interpretation timeline
2 Kings 22:8 Douay-Rheims

And Helcias the high priest said to Saphan the scribe: I have found the book of the law in the house of the Lord: and Helcias gave the book to Saphan, and he read it.

A.D. 850 – 1875 7 witnesses

Medieval

c. 750 – 1100
850
A.D.
Ishodad of Merv Medieval
d. A.D. 850
“The book that was discovered was the Deuteronomy that Moses had placed in the ark as a precaution. It was brought out through a divine action, in order to show the people that it cried and argued against them because of their great iniquity and therefore did not want to stay in its place. Hilkiah, who found the book, was the father of the prophet Jeremiah. It is not without a reason that the book was discovered at the time of Josiah because he, more than all the other kings, showed a real fervor against the priests of Baal, especially against those of the ten tribes, that is, those that had survived among them. Indeed, if [the book] had been found at the time of the other kings, they would not have accepted it. They might have even torn it up, as Zedekiah tore the prophecy of Jeremiah and threw it into the fire. [Another reason] is that the time of their captivity had come. For the seventy years of the Babylonian captivity are usually counted from the eighteenth year of Josiah, the year in which the book was discovered: as if the captivity was about to come in those days but was hindered because of Josiah's virtue.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“I have found the Torah Scroll. It was hidden under a layer of stones where they had concealed it when Achaz burned the Torah.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And Hilkiah the high priest said unto Shaphan the scribe,.... Not at the first time of his message to him, but afterwards that he attended on him upon the same business; after the high priest had examined the temple to know what repairs it wanted, and where: I have found the book of the law in the house of the Lord; some think this was only the book of Deuteronomy, and some only some part of that; rather the whole Pentateuch, and that not a copy of it, but the very autograph of Moses, written with his own hand, as it seems from Ch2 34:14. Some say he found it in the holy of holies, on the side of the ark; there it was put originally; but, indeed, had it been there, he might have found it before, and must have seen it, since, as high priest, he entered there once every year; more probably some pious predecessor of his had taken it from thence in a time of general corruption, as in the reign of Manasseh, and hid it in some private place, under a lay of stones, as Jarchi, in some hole in the wall, which upon search about repairs was found there: and Hilkiah gave the book to Shaphan, and he read it; and though there might be some copies of it in private hands, yet scarce; and perhaps Shaphan had never seen one, at least a perfect one, or however had never read it through, as now he did.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“I have found the book of the law - Was this the autograph of Moses? It is very probable that it was, for in the parallel place; Ch2 34:14, it is said to be the book of the law of the Lord by Moses. It is supposed to be that part of Deuteronomy (28, 29, 30, and 31), which contains the renewing of the covenant in the plains of Moab, and which contains the most terrible invectives against the corrupters of God's word and worship. The rabbins say that Ahaz, Manasseh, and Amon endeavored to destroy all the copies of the law, and this only was saved by having been buried under a paving-stone. It is scarcely reasonable to suppose that this was the only copy of the law that was found in Judea; for even if we grant that Ahaz, Manasseh, and Amon had endeavored to destroy all the books of the law, yet they could not have succeeded so as to destroy the whole. Besides, Manasseh endeavored after his conversion to restore every part of the Divine worship, and in this he could have done nothing without the Pentateuch; and the succeeding reign of Amon was too short to give him opportunity to undo every thing that his penitent father had reformed. Add to all these considerations, that in the time of Jehoshaphat teaching from the law was universal in the land, for he set on foot an itinerant ministry, in order to instruct the people fully: for "he sent to his princes to teach in the cities of Judah; and with them he sent Levites and priests; and they went about through all the cities of Judah, and taught the people, having the book of the Lord with them;" see Ch2 17:7-9. And if there be any thing wanting to show the improbability of the thing, it must be this, that the transactions mentioned here took place in the eighteenth year of the reign of Josiah, who had, from the time he came to the throne, employed himself in the restoration of the pure worship of God; and it is not likely that during these eighteen years he was without a copy of the Pentateuch. The simple fact seems to be this, that this was the original of the covenant renewed by Moses with the people in the plains of Moab, and which he ordered to be laid up beside the ark; (Deu 31:26); and now being unexpectedly found, its antiquity, the occasion of its being made, the present circumstances of the people, the imperfect state in which the reformation was as yet, after all that had been done, would all concur to produce the effect here mentioned on the mind of the pious Josiah.”
Source
1849
A.D.
1774–1849
“The book of the law, (that is, Deuteronomy.; Challoner.; St. Chrysostom, hom. 9. in Matthew) or the Pentateuch. (Josephus) — Achaz, Manasses, and Amon, had burnt (R. Solomon) as many copies as they could, (Haydock) but some zealous priests had concealed this copy, in a box, in the wall of the temple, (Lyranus) or in the treasury adjoining it. The very hand writing of Moses, containing the record of the covenant, (or the 28, 29, 30, and 31st chapters of Deuteronomy) which was placed in (Calmet) or beside the ark, was now happily discovered. (Haydock) — It seems it had been misplaced, as the ark itself had been removed, 2 Paralipomenon xxiv. 14., and xxxv. 3. This venerable monument, and the dreadful menaces which it denounced, made the deepest impression upon all, as we should read the autographs of St. Matthew, &c., with far greater respect and emotion than we do the printed copies. It is not at all probably that all the books of Scripture had been destroyed, as there were always some religious souls in both kingdoms; and if some kings had already made the impious attempt, (Haydock) of which, however, they are never accused in Scripture, they would not have been able to carry their malicious designs into effect. Josias had, before his 18th year, made many excellent regulations, conformably to the law, which was well understood, and carefully preserved by the priests and prophets, (Calmet) 2 Paralipomenon xvii. 9. — Read it. Scribes were generally chosen from among the Levites. (Calmet)”
Source
1871
A.D.
1871
“HILKIAH FINDS THE BOOK OF THE LAW. (Kg2 22:8-15) Hilkiah said . . . I have found the book of the law in the house of the Lord, &c.--that is, the law of Moses, the Pentateuch. It was the temple copy which, had been laid (Deu 31:25-26) beside the ark in the most holy place. During the ungodly reigns of Manasseh and Amon--or perhaps under Ahaz, when the temple itself had been profaned by idols, and the ark also (Ch2 35:3) removed from its site; it was somehow lost, and was now found again during the repair of the temple [KEIL]. Delivered by Hilkiah the discoverer to Shaphan the scribe [Kg2 22:8], it was by the latter shown and read to the king. It is thought, with great probability, that the passage read to the king, and by which the royal mind was so greatly excited, was a portion of Deuteronomy, the twenty-eighth, twenty-ninth, and thirtieth chapters, in which is recorded a renewal of the national covenant, and an enumeration of the terrible threats and curses denounced against all who violated the law, whether prince or people. The impressions of grief and terror which the reading produced on the mind of Josiah have seemed to many unaccountable. But, as it is certain from the extensive and familiar knowledge displayed by the prophets, that there were numbers of other copies in popular circulation, the king must have known its sacred contents in some degree. But he might have been a stranger to the passage read him, or the reading of it might, in the peculiar circumstances, have found a way to his heart in a manner that he never felt before. His strong faith in the divine word, and his painful consciousness that the woeful and long-continued apostasies of the nation had exposed them to the infliction of the judgments denounced, must have come with overwhelming force on the heart of so pious a prince.”
Source
1875
A.D.
Keil & Delitzsch Lutheran
1861–1875
“Hilkiah the high priest (cf. Ch2 34:15) said, "I have found the book of the law in the house of Jehovah." התּורה ספר, the book of the law (not a law-book or a roll of laws), cannot mean anything else, either grammatically or historically, than the Mosaic book of the law (the Pentateuch), which is so designated, as is generally admitted, in the Chronicles, and the books of Ezra and Nehemiah. (Note: Thenius has correctly observed, that "the expression shows very clearly, that the allusion is to something already known, not to anything that had come to light for the first time;" but is he greatly mistaken when, notwithstanding this, he supposes that what we are to understand by this is merely a collection of the commandments and ordinances of Moses, which had been worked up in the Pentateuch, and more especially in Deuteronomy. For there is not the smallest proof whatever that any such collection of commandments and ordinances of Moses, or, as Bertheau supposes, the collection of Mosaic law contained in the three middle books of the Pentateuch, or Deuteronomy 1-28 (according to Vaihinger, Reuss, and others), was ever called התורה ספר, or that any such portions had had an independent existence, and had been deposited in the temple. These hypotheses are simply bound up with the attacks made upon the Mosaic authorship of the Pentateuch, and ought to be given up, since De Wette, the great leader of the attack upon the genuineness of the Pentateuch, in 162a of the later editions of his Introduction to the Old Testament, admits that the account before us contains the first certain trace of the existence of our present Pentateuch. The only loophole left to modern criticism, therefore, is that Hilkiah forged the book of the law discovered by him under the name of Moses, - a conclusion which can only be arrived at by distorting the words of the text in the most arbitrary manner, turning "find" into "forge," but which is obliged either to ignore or forcibly to set aside all the historical evident of the previous existence of the whole of the Pentateuch, including Deuteronomy.) The finding of the book of the law in the temple presupposes that the copy deposited there had come to light. But it by no means follows from this, that before its discovery there were no copies in the hands of the priests and prophets. The book of the law that was found was simply the temple copy, (Note: Whether the original written by Moses' own hand, as Grotius inferred from the משה ביד of the Chronicles, or a later copy of this, is a very superfluous question; for, as Hvernick says, "even in the latter case it was to be regarded just in the same light as the autograph, having just the same claims, since the temple repaired by Josiah was the temple of Solomon still.") deposited, according to Deu 31:26, by the side of the ark of the covenant, which had been lost under the idolatrous kings Manasseh and Amon, and came to light again now that the temple was being repaired. We cannot learn, either from the account before us, or from the words of the Chronicles (Ch2 34:14), "when they were taking out the money brought into the house of Jehovah, Hilkiah found the book of the law of the Lord," in what part of the temple it had hitherto lain; and this is of no importance so far as the principal object of the history is concerned. Even the words of the Chronicles simply point out the occasion on which the book was discovered, and do not affirm that it had been lying in one of the treasure-chambers of the temple, as Josephus says. The expression ויּקראהוּ does not imply that Shaphan read the whole book through immediately.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.