The Pistis Sophia is one of the more well-known of the early Gnostic writings. Currently, scholars date it to the 4th or 5th century, but really, its origins are unknown. We have no reason to doubt that their guess is a good one, but it's nonetheless a guess. More radical historians have assigned it to a time period as early as the 2nd century or as late as the 10th.
If you're interested in details about this, gnosis.org has a thorough introduction to the text, as well as the entire text.
I don't know how else to put this except to say that the things said in popular Gnostic writings—such as the Pistis Sophia—are nonsense. All three of the above mentioned writings are prone to paradoxical statements that are supposed to be profound, but they're clearly just pious claptrap.
In case that's too easy to understand or to put into application in your life, try this one:
I'm terribly sorry, but this excerpt from the Pistis Sophia sounds like a bad translation from one of those online automatic language translators. It doesn't mean anything at all!
The one thing that stands out as I read these gnostic writings is that there's not a practical application in sight. These are the sorts of things you might chant in a dark room at night with candles, but there's nothing at all you can do with them except claim special spiritual insight if you can understand a word!
The most important part of the Pistis Sophia is not the teachings in it. It's the oft-repeated line: "Jesus had not told his disciples."
The one great argument that early Christian apologists had against the gnostics was that they were not descended from the apostles. Jesus committed his Gospel to the apostles, say all the early Christians, and those who claim to speak for Jesus against the apostles are false.
The Pistis Sophia says repeatedly in its first chapter that there were things that Jesus had not told his disciples. This was exactly the argument of all gnostic teachers, who were able to teach whatever they wanted, upon their own authority, because Jesus had secret knowledge, they said, which he hid from the apostles.
Irenaeus says of the gnostics:
Irenaeus objects to this, of course. He argues:
The gnostics disagree with this. They argued that important and secret knowledge had come to them through other means. In the Gospel of Mary that knowledge was passed through Mary Magdalene. Others found different sources. Either way, the knowledge was always something that either the apostles or the apostles' churches did not know about.
But what sort of knowledge was that? What were these mysteries delivered to these gnostic teachers?
According to the Pistis Sophia, Jesus had not told his disciples …
He also had not told them, "I have gone forth out of such and such regions until I entered into that mystery, and until I went forth out of it."
Good luck figuring out how any of that is going to affect your behavior, if you can even figure out what any of it means. No, it's not explained in the Pistis Sophia.
Now that you know that Jesus didn't tell the apostles about the total expansion of the emanations of the Treasury, what do you intend to do differently? And once you find out what the region is of the seven Amens, what changes will you make in your life?
I apologize for the sarcasm, but there is a point I am trying to make …
Justin Martyr once said that Jesus was no philosopher. "Brief and concise utterances fell from his lips … his words were the power of God." (First Apology 14).
From the time that Jesus first said, "You shall know them by their fruit" (Matt. 7:16) the apostles—and the apostolic churches—defended the Gospel with their lives. When Paul was called to account for his Gospel, he said, "I am not ashamed of the Gospel of Christ, for it is the power of God to salvation … for in it the righteousness of God is revealed from faith to faith" (Rom. 1:16-17).
Paul, in defending his Gospel, pointed to exactly what Jesus had pointed to: fruit. His Gospel produced a righteousness that could be seen.
The apostolic churches were the same way. Justin Martyr, quoted above, wrote the emperor defending Christianity by pointing out the holy lives Jesus taught Christians to live. Athenagoras, defending Christianity twenty years later, wrote:
It does not matter what early Christian apologists had to say about the behavior and lifestyle of gnostic teachers, nor whether what they said is accurate or inaccurate.
The fact is, the gnostic writings themselves—now that we've found them—teach us nothing at all about the practical obedience to God that is central to the teaching of Jesus and the apostles, and to the churches the apostles founded.
Popular authors today are trying to rewrite the history of Christianity, arguing that orthodox Christians triumphed by chance, then suppressed the truth about the various forms of gnosticism. Far from it. They wrote accurately about the gnostics.
A number of gnostic writings have surfaced in the last couple centuries, such as the Pistis Sophia, and they give us the real reason orthodox Chrisitanity triumphed. It received the Gospel and power of the apostles who were backed by God because they taught people to obey God. Gnosticism, on the other hand, was simply a wildly fanciful and utterly impractical form of Greek philosophy that could not last.