Guillaume Félice, History of the Protestants of France, pp. 351-352:
David Blondel (1595-1655) was the man of his times the most versed in ecclesiastical history. His prodigies of memory are related; he read every thing, and forgotten nothing. Having become blind, he dictated two folio volumes on difficult points of chronology and antiquities. The National Synod gave him the title of honorary professor, without attaching him to any academy, and all the provinces gave him an annual pension for his maintenance at Paris.
Blondel combated the pretensions of the See of Rome to the primacy, the false decretals, and the Sibylline oracles. His good faith equalled his erudition; he was blamed by a few old Huguenots for having contradicted the legend of the Popess Jeanne, which they maintained so fondly.
To elaborate on those four particulars:
1. Primacy of Rome. Blondel wrote De la primauté en l'Eglise (1641), one of his most important works, to challenge the arguments for the primacy of the Roman see over the rest of Christendom, such as the claim that Peter was in Rome. He wrote another work in 1646, a the behest of the Westminster Assembly, against episcopacy and in favor of Presbyterianism: Apologia pro sententia Hieronymi de episcopis et presbyteris.
2. False Decretals. Under the pseudonym Isidore Mercator, a ninth-century collection of purported papal decretals and letters from the early church era, known now as Pseudo-Isidore, or the False Decretals, was generated, the thrust of which was to provide historical precedents for papal claims to temporal power. For example, the "false decretals attributed to early martyr-popes declare it forbidden so much as to accuse a bishop of a crime, and that eternal damnation and hell awaits anyone who would dare prosecute a bishop." Certain Catholic and Protestant scholars, such as Cardinal Nicholas of Cusa and Lutheran Matthias Flacius Illyricus and his Centuriators of Magdeburg, pointed out historical discrepancies and anachronisms within the body of documents, but David Bondel was the first to show systematically that the decretals were forgeries by pointing out that some of the alleged early papal writers quoted from authors who wrote much later. His 1628 Pseudoisidorus et Turrianus vapulantes effectively destroyed forever the belief that the decretals were genuine.
3. Sybilline Oracles. A collection of twelve books of ecstatic prophetic utterances attributed to the Sibyls, not the earlier Roman prophetesses whose utterances comprise the Sybilline Books, but others said to be of Judeo-Christian origin from the second to the fifth century. Matthew Henry writes:
The oracles of the Sibyls were appealed to by many of the fathers for the confirmation of the Christian religion. Justin Martyr appeals with a great deal of assurance, persuading the Greeks to give credit to that ancient Sibyl, whose works were extant all the world over; and to their testimony, and that of Hydaspis, he appeals concerning the general conflagration and the torments of hell. Clemens Alexandrinus often quotes the Sibyls' verses with great respect; so does Lactantius; St. Austin, De Civitate Dei, has the famous acrostic at large, said to be one of the oracles of the Sibylla Erythrea, the first letters of the verses making Iesous Christos Theou hyios Soter—Jesus Christ the Son of God the Saviour. Divers passages they produce out of those oracles which expressly foretel the coming of the Messiah, his being born of a virgin, his miracles, his sufferings, particularly his being buffeted, spit upon, crowned with thorns, having vinegar and gall given him to drink, &c. Whether these oracles were genuine and authentic or no has been much controverted among the learned. Baronius and the popish writers generally admit and applaud them, and build much upon them; so do some protestant writers; Isaac Vossius has written a great deal to support the reputation of them, and (as I find him quoted by Van Dale) will needs have it that they were formerly a part of the canon of scripture; and a learned prelate of our own nation, Bishop Montague, pleads largely, and with great assurance, for their authority, and is of opinion that some of them were divinely inspired. But many learned men look upon it to be a pious fraud, as they call it, concluding that those verses of the Sibyls which speak so very expressly of Christ and the future state were forged by some Christians and imposed upon the over-credulous.
Rieuwerd Buitenwerf, Book III of the Sibylline Oracles and Its Social Setting, pp. 17-18, writes:
Around the middle of the seventeenth century, claims concerning the origins of the extant Sibylline Oracles became a trump card in the quarrels between Catholic and Protestant theologians. In 1649 David Blondel (1591-1655), a Calvinist theologian and professor of history in Amsterdam, published a study about the historical background of Sibylline literature. The main purpose of his work, Des Sibylles célébrées, was to wipe the floor with all those who believed in the authenticity of the eight books attributed to the Sibyls. In the first part of his work, Bondel systematically discusses pagan and early Christian testimonies of the Sibylline oracles. According to Bondel, these testimonies are spurious or based on foolish superstition.
Bondel himself was convinced that the Sibylline books were Christian forgeries, devoid of any divine inspiration. His fury made him declare, for instance, that the Sibylline prophecies are jabber, uttered by a fanatic. He also remarks that the original Roman Sibylline books were destroyed in a fire.
The second part of Blondel's book deals mainly with the Roman Catholic practice of praying for the deceased. According to Bondel, four basic suppositions found in the Sibylline Oracles inevitably lead to this practice. The first supposition is that all humans descend to hell and stay there until the day of resurrection (see, for example, Sib. Or. I 81-86). The next is that the world will be destroyed by fire on Judgment day. According to the Roman Catholics, this fire serves as a purgatory for the souls and bodies of the saints (see, for instance, Sib. Or. II 315-318 and III 286-287). The third supposition is that paradise, which is still in existence somewhere on earth, functions as a resting place for the saints (see, for example, Sib. Or. fr. iii 46-49). The last supposition is that there will be a temporary kingdom of bliss, which will be established by the Lord and will precede the day of Judgment (see, for instance, Sib. Or. III 619-623). The combination of these four ideas which occur in the Sibylline Oracles, led many Fathers of the Church, as well as the Roman Catholics, to believe that it might be useful to pray for those who have died, since prayer was supposed to improve their fate on Judgment day. According to Blondel, however, the Sibylline books must be considered frauds: they cannot be used in justification of the Roman Catholic practice of praying for the deceased.
4. Pope Joan. A story, which has been traced to the twelfth century, claims that between Popes Leo III and Benedict III in the ninth century, a female pope sat on "St. Peter's chair" for a two-year period. She was also said to have actually delivered a baby while attempting to mount a horse while on the street now known as Vicus Papissa. Adding to the story, a chair with a hole in it was said to be used by papal officials until the 15th century in order to confirm the gender of elected popes. Others have placed her purported reign in the twelfth century, but regardless, the story was widely believed from that time on, and credited to the extent that she was included in a line of papal busts sculpted and displayed around 1400 at the Cathedral of Sienna, and identified as Johannes VIII, Femina ex Anglia, but later replaced by that of Pope Zachary. The tradition became an obvious source of embarrassment to the Roman Catholic Church, and Pope Clement VIII was forced to declare the story untrue in 1601. But, understandably, Protestant apologists have made hey over the story. The ninth century was the low point for the papacy, known as the Saeculum obscurum; in fact, it was so corrupt that some nineteenth century German historians have referred to this period, because of its promiscuous popes, as the Pornocracy. The idea of a female pope reigning over Christendom for two years during this undisputed "nadir" of the papacy was irresistible to those seeking to discredit the papacy during the Reformation. The legend of Pope Joan seemed tailor-made for those who mocked the Catholic Church and its hall of shames.
However, David Blondel believed that if the story was false, it did the Protestant cause no good to hammer the point. Blondel wrote Familier Eclaircissement de la Question, Si une femme a esté assise au Siege Papal de Rome entre Leon IV & Benoist III (1647) with a view towards deconstructing the myth by showing that it was impossible that she reigned during the ninth century period alleged. His theory is that the legend itself grew from a satire about Pope John XI, another ninth century pope.
Alain Boureau, The Myth of Pope Joan, pp. 251-252:
David Blondel, a Calvinist pastor, published a refutation of the history of Joan that many Protestants considered a betrayal of their cause: Familier esclaircissement de la Question si une Femme a este assise au Siege Papal de Rome entre Leon IV et Benoit III (Familiar Clarification of the Question of Whether a Woman Sat on the Papal Throne of Rome between Leo IV and Benedict III). This work was reprinted in 1649 and was translated into Dutch in 1650 and into Latin in 1657.
In 1647 David Blondel's Familier eclairissement was by no means an attempt to reach out to Catholicism. His scornful point was that Rome of his own day had enough demonstrable crimes and heresies without being reproached for a heavy dossier of dubious fables as well.
His treatise resulted in accusations by fellow Huguenots that he had been bought off by the other side with a pension from the king of France.
Michel de la Roche, Memoirs of Literature, Vol. 3, p. 387-388:
David Blondel, a very learned Man, being fully persuaded that the Story of Pope Joan was a mere Forgery, was so sincere as to write against it. Some took him to be a false Brother upon that account. They were strangely surprised to see that Story, on which they laid so great Stress, confuted by a Protestant Minister. I must observe that Blondel did actually receive at that time a yearly Pension of a thousand Crowns from the King of France; which was sufficient to raise some Suspicions against him. The Readers will not be displeased to know upon what account he received that Pension; and therefore in order to satisfy their Curiousity, I must beg Leave to make a short Digression.
John James Chifflet having published a learned Book in favour of the House of Austria, containing several things disadvantageous to the House of France, the Cardinal expressed a great desire to have it confuted. He sent for Petavius, and desired him to answer it. That Jesuit told his Eminence, That he was not sufficiently acquainted with the History of France; and that he knew but one Man in the Kingdom that was able to write against Chifflet. The Cardinal asked him, who he was. Blondel, said Petavius. Blondel, replied the Cardinal: He is a Huguenot: He is a Minister. My Lord, continued Petavius, he is the only Man that I can recommend for such a Performance. The Cardinal, being unwilling to employ a Protestant, sent for Father Sirmond and desired him to write against Chifflet. Father Sirmond replied, that he was not sufficiently skilled in the History of France, to undertake such a Work; and that he knew but one Man that could do it with good Success. Who is he? said the Cardinal. Blondel, replied Father Sirmond. The Cardinal having consulted those two learned Men, found himself obliged to make use of Blondel. Whereupon a Pension of a thousand Crowns was immediately assigned to that learned Minister, to write in favour of the House of France.
It was then that Blondel published his Treatise concerning Pope Joan; from whence some Zealots inferred that he had been bribed by the Court of France to write upon that Subject. But their Suspicions were altogether groundless. Blondel was a true Protestant, and died in the Communion of the Reformed Churches. Some are of the opinion, that he did a good Service to the Protestant Churches of Rance, by confuting that Story.