Some fragments from the lost Gospel of Thomas containing a few sayings attributed to Jesus were unearthed by the papyrologists Bernard Pyne Grenfell and Arthur Surridge Hunt. These sayings were part of an impressive cache of literature composed in Greek that was discovered at Oxyrhynchus, Egypt back in 1897. They published a translation of this Jesus material in a book called, The Sayings of Our Lord.
Those verses of Christ not present in the New Testament gospels were not in any way associated with anything gnostic during those days.
It wasn’t until the entire Gospel of Thomas with all one hundred and fourteen sayings was found along with many other texts in 1945 at Nag Hammadi, Egypt did the word gnostic get associated with this particular collection of the sayings of Yeshua. Since this book of Thomas was one of many included in this discovery, predominately consisting of Valentinian and Sethian gnostic scriptures, most came to view the Gospel of Thomas as being gnostic too.
Of course there are many examples of non-gnostic writings part of the same Nag Hammadi discovery such as the book of the Sentences of Sextus the Pythagorean, also the proto-orthodox Teachings of Sylvanus, some Hermetic material, and even a section of Plato’s Republic. Nevertheless a kind of “guilt by association” in the minds of some have lead to this perception of the Gospel of Thomas, a collection of the sayings of Jesus, as somehow being the composition of some later gnostic sect.
The Gospel of Thomas was not a gnostic text in my view, not the creation of a Valentinian or Manichaean author, in other words. No doubt some gnostic groups such as the Valentinians and Sethians perhaps liked it. They were also fans of the Gospel of John, a book not usually labeled as “gnostic” by most.
The compiler of the Gospel of Thomas was one of the few who had access to the Q/source material, a collection of saying of Jesus evidently used by some of the early composers of gospels.
The author of the Gospel of Luke said “many” had already written gospels before he decided to also write his. “Now many have undertaken to organize an account of the events fulfilled among us, just as they were handed down to us from the start by the eyewitnesses and reporters of the word.” (Gospel of Luke, 1: 1 and 2)
There seems to also be some overlap between the book of Thomas and another very early text called the Gospel of the Hebrews, with some shared sayings. “As also it stands written in the Gospel of the Hebrews: ‘He that marvels shall reign, and he that has reigned shall rest.’” (Clement of Alexandria, early church father, Stromateis 126.96.36.199) There’s a longer version of that saying also in Stromateis that’s more in line with the Greek Gospel of Thomas fragments found by Grenfell and Hunt: “He that seeks will not rest until he finds; and he that has found shall marvel; and he that has marveled shall reign; and he that has reigned shall rest.” (See saying 2 of the Gospel of Thomas)
Some of those Thomas sayings of Jesus also apparently got included in the original Tatian’s Gospel Harmony (Diatessaron). (see, The Gospel of Thomas, Introduction and Commentary, by Simon Gathercole)
What we think of as “Thomasonian” sayings of Jesus also turn up in many other interesting places, were known by many, which I find utterly fascinating, as it shows that the sayings preserved in Thomas have a very real, complicated and authentic history behind them, were quoted far and wide in antiquity!
Saying 52 of the GoT is found in the writings of Saint Augustine. “But when the apostles asked what should be thought about the prophets of the Jews, who were thought to have sung something in the past about his coming, he was disturbed that they should still think such things, and replied: ‘You have abandoned the Living One who is before you, and are talking about the dead.’” (Against the Adversary of the Law and the Prophets 2.4.14)
Origin of Alexandria quoted saying GoT 82: “”He who is near me is near the fire, and he who is far from me is far from the kingdom.”
Saying 113 turns up in the writings of Saint Macarius of Syria: “As the Lord has said, ‘The Kingdom of God is spread out on the earth, and people do not see it.’” Macarius quoted other Thomas-Jesus verses as well.
There are many parallel sayings — Thomasonian Jesus sayings — that turn up in the contemplative mystical tradition of Christianity of the Syriac east. I agree with those who have the view that the Gospel of Thomas was composed just north of Israel in Syria, was one of several books attributed to Saint Thomas, and that the true home of the Gospel of Thomas is in this Mesopotamian Syriac tradition of the Church of the East characterized by the scholar Bentley Layton as “the School of Saint Thomas”.
Layton also observes: “Since there is nothing especially sectarian about the Thomas scripture, it must have been a part of the normal canon of scripture read by Mesopotamian Christians in the second and early third centuries. It would have been read along with works such as the Odes of Solomon and Tatian’s Harmony (Diatessaron).” (The Gnostic Scriptures, Bentley Layton and David Brakke)
There are many more such examples of sayings of Jesus associated with the Gospel of Thomas that are to be found in early Christian writings, New Testament apocrypha, the Ebionite Clementine literature, The Heliand or Saxon Gospel (which seems to have been unfluenced by an early unredacted Tatian’s Gospel Harmony), also writings of early church fathers. There’s a great book with a handy collection of many of these parallels in other texts called, Extracanonical Sayings of Jesus, by William D. Stroker.
The Gospel of Thomas was liked and quoted by gnostics, yes, but is not necessarily a book composed by gnostics just because a copy of it was included in the Nag Hammadi Library.
For a great book discussing how the teachings present in the Gospel of Thomas fit into the world of Kabbalah and Christian mysticism, see, The Gospel of Thomas in the Light of Early Jewish, Christian and Islamic Esoteric Trajectories, by Samuel Zinner.