What basis could there be for an 18th century Christian to say that "Gnostics were the Antinomians of their day"?

My search about this guy using perplexity.ai:

Augustus Toplady was an Anglican cleric and hymn writer who was a major Calvinist opponent of John Wesley. He believed that anyone who denied predestination was a blasphemer and had harsh words for Methodist theology. In 1758, Toplady became an extreme Calvinist and published his translation of Zanchius's Confession of the Christian Religion (1562), which convinced him to become a Calvinist. His works include The Doctrine of Absolute Predestination Stated and Asserted (1769), A Treatise on the Doctrine of Election (1770), and Hymns Concerning the Doctrine of Election (1771).

I don't think that quote "An Antinomian looks to be justified by his works" is accurate, as it doesn't show in any web search, but it is also oxymoron, since antinomians are by definition lawless, licentious, libertine people who oppose the law of God, they hate works and righteousness. The actual quote by Toplady is the following, that I found, The Works of Augustus Toplady Vol 3, p.185:

(Sermon IX) The Existence and Creed of Devils Considered:
Against this most dangerous delusion, the blessed apostle James drew his pen. And the principal drift of this epistle, is, not to counteract St. Paul (for all the divine writers speak one uniform, harmonious language): but, merely to show the delusion which the Gnostics, who were the Antinomians of that age, were under; and to prove, that mere head knowledge, is requisite to stamp us heirs of God, and joint heirs with Christ. Hence we find the apostle, at the 14th verse, asking, What does it profit, my brethren, though a man say he hath faith, and hath not works? Can faith save him? Observe, with what caution St. James expresses himself. He does not say, "what will it profit a man, to have faith without works? for he knew that to be impossible. But the words are, What will it profit a man, to say that he hath faith, without works? There is a vast difference, between believing, and saying we believe.

[....] A Mahometan expects to be saved by his works. A Socinian thinks to go to heaven by his works. A Papist looks to be justified by his works. A Free-willer hopes for salvation by his works, compliances, endeavours, and perseverance. A Pagan, if he believes that there is a future state, expects to be happy hereafter, by virtue of the supposed good he does, and of the evil he leaves undone. A Mystic has the same hope, and stands on the same sad foundation. It is only the religion of Christ, which runs counter to all the rest, by affirming, that we are saved, and called with an holy calling, not according to our works, but according to the Father's own purpose and grace, which was [not sold out to us on certain conditions to be fulfilled by ourselves, but was] given us, in Christ, before the world began (a). It was long ago remarked by a good man, that "It is the business of all false religions, to patch up a righteousness, in which the sinner is to stand before God." But it is the business of the glorious Gospel, to bring near to us, by the hand of the holy Spirit, a righteousness ready wrought; a robe of perfection ready made; wherein God's people, to all the purposes of justification and happiness, stand perfect and without fault before his throne.

I'd agree with him on this quote which relates the early Gnostic licentious heretics among Gentiles as lawless, or rightly antinomian. This is concerning the moral law, not the Moses law.

Those in hurry can just ignore the following background details and analysis on Gnosticism, which I thought was essential to study the topic with sources.

Gnosticism is essentially a term used to describe the ancient cults which questioned the objective nature of truth, and attempted to go beyond reality by inventing alternative myths. It seems to be some sort of ancient roots of counter culture; an escape from reality. They emphasize on existential questions and enlightenment. The eastern philosophies of India like Zen Buddhism and Dvaita Vedanta can be linked to it. Their purpose of attaining enlightenment and ridding ignorance is by denying reality of the world, including human suffering. They turned their back on physical matter altogether. They believed the world or the physical matter is a product of an inferior god, therefore evil or inherently tainted and corrupt. Their gods included Monad, the invisible hidden god, and others such as Abraxas. Gospel of Philip, a Gnostic gospel showed an alternative reality of Jesus escaping from death and someone else took his place, because God was too powerful and detached from the world to really become a man. These same narrative was later found in the Syrian Nasara (Gnostic) Quran, which was later modified into the Islamic Quran.

When Christianity emerged it the Gnostic masses easily adopted it. The Gnostics view free will as an illusion created by human experience, and believe that man's natural inability and predestination are opposed to self-redemption by one's own means alone. The doctrines of original sin, condemnation of matter as sin; reducing sin as a metaphysical inborn sickness in the flesh and soul rather than moral transgression (moral realism) makes us conclude that early Roman church was heavily influenced by Gnosticism. Augustin, who belonged to a Gnostic sect as a Manichaean priest and converted to the Church to save his life eventually failed to fully convince the Church against freewill. Note that the hallmarks of Gnostic philosophy are denial of objective reality such as freewill, belief in a fatalistic predestination, condemning mankind as inherently evil and depraved to suppressing the moral conscience. Consequently, such doctrine cannot accept the full or true incarnation of God as Jesus.

Marcion belonged to the sect of Gnosticism who unlike Augustin, openly condemned the God of OT. He was actually distinguished for his view of dividing the God of the bible into two by saying the OT was revealed by an inferior evil god. This is what makes him so different from the mainstream accepted Gnostic beliefs, since he did not attempt to create a rationalized harmony or balance with Christianity, as Martin Luther did after facing criticism. We can find here the best distinction of honest and crafty kinds of gnosticism. Johannes Agricola being a more honest Gnostic antinomian, could not gain popularity in that time.

Martin Luther preached sin to others, exalted the view of total depravity of the flesh as inherently corrupt, thereby ridding of moral responsibility which condemns the law of God. He also openly argued against Reason or logic itself, calling it "the devil's greatest who*e".

We see grain sowed in the ground. Reason now asks: What happens to the grain in winter that has been sowed in the ground? Is it not a dead, moldy, decayed thing, covered with frost and snow? (Luther's sermon On our Blessed hope)

Conceived in sorrow and corruption, the child sins in his mother’s womb. As he grows older, the innate element of corruption develops. Man has said to sin: ‘Thou art my father’—and every act he performs is an offense against God; and to the worms: ‘You are my brothers’—and he crawls like them in mire and corruption. He is a bad tree and cannot produce good fruit; a dunghill, and can only exhale foul odors. (Werke, (Wittenberg Edition), Vol. III, p. 518.)

Luther managed to find an apologetic balance with the scriptures with attempts to rationalize the commands/justice with his doctrines. However, not every follower of Luther was not easily going to follow along, the pushback was bound to happen. The first major controversy broke perhaps in the 17th century, known as Antinomian controversy:

The Antinomian Controversy, also known as the Free Grace Controversy, was a religious and political conflict in the Massachusetts Bay Colony from 1636 to 1638. It pitted most of the colony's ministers and magistrates against some adherents of Puritan minister John Cotton. The most notable Free Grace advocates, often called "Antinomians", were Anne Hutchinson, her brother-in-law Reverend John Wheelwright, and Massachusetts Bay Governor Henry Vane. The controversy was a theological debate concerning the "covenant of grace" and "covenant of works".

These modern Antinomians attempted to refine the core dogma of the reformation movement, by riding the artificial apologetic shield that permitted moral responsibility and importance of the law/commandments. The same reformation pushback is often called "Hyper Grace" movement today. Paul Ellis is one of those honest refined protestant preachers whose articles can be very helpful to understand the modern Antinomianism; his website is ironically named 'escape to reality'.

Coming back to Toplady, he was a calvinist contributor of the Free Grace movement aka Antinomian sect. He was the one labelled as an Antinomian perhaps by some liberal Calvinist brothers; I doubt that he himself ever practically judged any man as being lawless. From a Baptist site:

The leading contestants in the Calvinistic-Arminian controversy were mainly Oxford and Cambridge dons and men of a first class education. The opposite was the case in the bitter debate concerning the Law which came to be referred to as the Antinomian Controversy. William Huntington (1745-1813), who took the side of the Law as God’s eternal standard, had a mere few months’ schooling and before becoming a pastor, was a coalman’s labourer. Andrew Fuller (1754-1815) who took up the cudgels for an abolition of the Covenant of Works and a Law emptied of its condemning and commanding power, was raised on a farm, received very little education and became a well-known pugilist before his days as a controvercialist.

Unlike in the Calvinistic-Arminian debate, both sides in the Antinomian Controversy professed to be Calvinists. Huntington held four-square to the doctrines of the Reformation regarding the Gospel and the Law whereas Fuller called himself an ‘evangelical Calvinist’ and reacted strongly against what he called Hyper-Calvinism.. He said of the Church before he left traditional Calvinism, “When I first published my treatise on the nature of faith, and the duty of all men who hear the gospel to believe it, the Christian profession had sunk into contempt amongst us; insomuch that had matters gone on but a few years longer, the Baptists would have become a perfect dunghill in society.” His aim in life was thus plain, “to rescue the Christian profession from being contemptible and save the Baptists from being a dunghill in society.”

Toplady, despite blaspheming God by blaspheming his holy laws (be it the Moses law or the eternal moral law) wrote in defense that he is not an antinomian. He described the licentious doctrines of antinomians, and claimed to denounce immorality- A Description of Antinomianism:

Practical Antinomianism is the habitual, allowed, and persevering violation of those precepts, which God hath prescribed for the adjustment of our outward conduct; whether those rules regard our demeanour toward him, toward our neighbour, or toward ourselves. Let a person's ideas be ever so orthodox, yet, if his life be immoral, he is, to all intents and purposes, a practical Antinomian, and unless the effectual grace of the holy Spirit intervene, to retrieve him from the dominion of his sins, he must after death be one of those, to whom Christ will say, "Depart from me; I never knew you, ye workers of iniquity."

In order to find out why A.M. Toplady linked Gnostics to Antinomians and justification by works, we need to go back to the Protestant Reformation. Here is an extract from an article which suggests that the father of antinomianism was Johannes Agricola (1494-1566):

Theologically, antinomianism is the belief that there are no moral laws God expects Christians to obey. An antinomian thinks he is under no obligation to follow any type of moral code. He is completely free. The father of antinomianism was Johannes Agricola. He, like Martin Luther, was a German Reformer, but they disagreed on whether the law permanently bound the Christian. Agricola’s position was that the purpose of the law was to drive Christians to the cross and repentance, at which point they were no longer under any law, either Levitical or moral. Luther, on the other hand, believed that the law had a place in the Christian’s life. The law initially drives a Christian to Christ, and it continues as a tool to move the believer to ongoing renewal and maturity. Luther publicly opposed Agricola’s teaching in “Against the Antinomians,” published in 1539. https://www.gotquestions.org/antinomian.html

Johannes Agricola, a German Protestant Reformer, was a follower and friend of Martin Luther, who became his antagonist in the matter of the binding obligation of the law on Christians. In 1536 he was recalled to teach in Wittenberg, and was welcomed by Luther. Almost immediately, however, a controversy, which had been begun ten years before and been temporarily silenced, broke out more violently than ever. Agricola was the first to teach the views which Luther was the first to stigmatize by the name Antinomian, maintaining that while non-Christians were still held to the Mosaic Law, Christians were entirely free from it, being under the gospel alone. After he wrote an attack on Luther (shortly after Luther had given him shelter when he was fleeing persecution), Luther had nothing further to do with him. https://en.wikipedia.org/wiki/Johannes_Agricola

Perhaps Toplady was familiar with the theological dispute between Johannes Agricola and Martin Luther on the question of the Mosaic Law and salvation. However, I am at a loss to understand why Toplady would say that “an Antinomian looks to be justified by his works." After all, Gnosticism claims that man is an inherently good soul trapped in the confines of an evil, material body and only needs to find the secret knowledge that will free him from his material body and reach God, who is good and perfect, but impersonal and unknowable.

Gnostics assert that matter is inherently evil and spirit is good. As a result of this presupposition, Gnostics believe anything done in the body, even the grossest sin, has no meaning because real life exists in the spirit realm only. On the matter of salvation, Gnosticism teaches that salvation is gained through the acquisition of divine knowledge which frees one from the illusions of darkness. Gnostics believe that Jesus’ physical body was not real, but only “seemed” to be physical, and that His spirit descended upon Him at His baptism, but left Him just before His crucifixion. https://www.gotquestions.org/Christian-gnosticism.html

It would seem that Gnostics think they can sin as much as they like, that they are not bound by any moral laws, least of all God’s laws, and so don’t need to be justified by works. Perhaps there is a sense that their salvation depends on their own efforts to attain this secret knowledge, and this may be seen as “works”. One thing is certain, the Gnostics who were around at the start of Christianity held a distinctly different view of the Bible, of Jesus Christ, of salvation, and of virtually every other major Christian doctrine. On the one hand Gnostics try to reach God by their own efforts, but on the other hand they reject the Christian doctrine that the only way to reach God is through his Son, Christ Jesus. Here is a possible link between Gnosticism and Antinomy:

In philosophy, the word antinomy is used to designate the conflict of two laws that are mutually exclusive or that oppose one another. When two carefully drawn, logical conclusions contradict each other, the result is antinomy. For example, the statement “There is no absolute truth” contains antinomy. The statement is self-contradictory. To say that a truth can never be absolute is opposed by the fact that the speaker is claiming to speak the truth. Does the assertion that there is no absolute truth apply to the assertion itself? Antinomy is the result of a finite being trying to grasp the infinite, and failing. https://www.gotquestions.org/antinomy.html

I have no idea what was going on in that acrimonious debate between Agricola and Luther back in the fourteenth century, but I suspect that Todplay (18th century) was onto something! As SLM concludes, "gnostics were the antinomians of their day".