Unfortunately the Catholic church rejected Christian Gnosticism because it concluded that Christian Gnosticism had adopted the premises of pagan Gnosticism.   

This lead to the Catholic creation of the trinity and the demotion of the Holy Spirit who is the Spirit Of Truth.   Think about how this served as a departure from true Christianity.   

God is Spirit and since He is the only God He is the Holy Spirit.   We see that Jesus was Fathered by the Holy Spirit.   

John the Baptist tells us that the purpose of Christ Jesus coming is that we could be baptized (immersed) into the Holy Spirit.   

By demoting the Holy Spirit and creating a Father God who is NOT the Holy Spirit the Catholics completely screwed up Christianity.   

They instituted rituals, catechisms and dogmas to replace the Truth of Christ Jesus with just another powerless religion.   

So, what is Christian Gnosticism?   

If we take the compound word and break it up into Christian and Gnosticism we see that it is nothing more, but very much:
   ➛ faith in the Gospel of Jesus Christ
   ➛ relationship with Christ as a New Creature

That needs a little expanding as there are various interpretations of what it means to have faith in the Gospel of Jesus Christ as well as what it means to be in a relationship with Christ and what exactly is the New Creature.   

By following the hyperlinks for the key words above you can fully understand what I summarize below:

When we believe that Jesus is the incarnation of the Word and Spirit of God identified in Joh 1:1 we pass the threshold of basic knowledge.   

When we recognize that repentance from a vain carnal life is necessary to enter into eternal, abundant life we pass the second threshold.   

When we actually repent and receive the knowledge of Christ Jesus based on who He is, what He did for us and what He wants us to be we are Born Again of His Word and His Holy Spirit becoming New Creatures who are New Spirit beings.   

When we ask the Lord to baptize us with Himself He fills us with His Holy Spirit and we begin a journey into growing in Grace and Knowledge of the Lord Jesus Christ through absorption of His Word and transformation by it through the understanding that is given us by His Holy Spirit Of Truth.   

It is in the immersion of ourselves into Christ that we experience the intimate personal relationship with Him.   

It is in this place that we experience Christian Gnosticism.   We don't just believe the Gospel, we know the Gospel is true because we know the One who it is all about.   

There are many who are believers in Christ who do not know the love of Christ or the Grace of Christ and so doubt their standing with Him.   

In Christian Gnosticism we know what we have believed by virtue of the Holy Spirit revelation of the Word.   We know intellectually just like the fearful but we also know spiritually and lose the fear by understanding the Love Of God that casts fear out.   

We also are imbued with sound minds, understanding that we are Sons Of God and not just sinners saved by Grace.   This knowledge makes us aware of our authority by Christ according to His Word and the power of Christ by His Holy Spirit.   

Christian Gnosticism is revelation knowledge, empowerment and awareness of who we are in Christ Jesus.   It is fathoming that we are a royal priesthood, superior to the Carnal Minded humans that make up society.   

Peter behaved like a Christian Gnostic on the Day Of Pentecost because He knew who Christ was and he knew who he was as Christ's Son and Apostle by Spiritual Revelation.   

Likewise the Apostle Paul was a Christian Gnostic because he demonstrated supernatural knowledge, self-control, courage and conviction spreading the Gospel among pagans while being attacked by unbelieving Jews.   His letters are filled with supernatural Truth by the Spirit Of Truth.   

In order to maintain control of Christianity the Catholic leaders determined that Holy Spirit filled Christians would be a problem as they would dream dreams, see visions, give Words of prophecy and messages in tongues.   Furthermore, the Holy Spirit Gifts manifesting through lay people would further reduce their control over the order of service, resulting in church splits.   

So, you end up with Catholicism.   

When the Protestant Reformation occurred there was not a general understanding of the scope of Catholic perversion from the Truth, and so much of Catholic dogma was carried forward limiting the power of the new churches to affect society.   

I daresay that if you claim to be a Christian Gnostic you would be uninvited from virtually every church because of ignorance and error in those churches.   

In closing, what completely separates Christian Gnosticism from pagan Gnosticism is that In Christ we are New Creatures who share His same Holy Spirit and we allow His Word to transform our minds and hearts.   

We bring nothing forward from our carnal selves.   The Old Man is dead and all things are new by virtue of Christ being our life with His Words, our Words and His deeds, our deeds.   

Humans are Spirit Soul And Body.   We are born with corrupted spirits based on Original Sin and so Christ Jesus came to enable us to be reborn as New Spirit beings who are His brothers born of the same Holy Spirit by the same Word.   We are dual beings in some sense as our minds must be transformed by the Words Of Christ to manifest as Sons Of God.   

At Christ's return our minds and bodies which are corruptible will be made incorruptible so there is no longer any hint of duality.   

However, gnostic is a good word which can be applied to anyone who has a knowledge of a subject that most people do not have.   

Contrast the word 'believer' with the word 'gnostic'.   
   ➛ a believer is an adherent because of conviction
   ➛ a gnostic is an adherent because of knowledge

We are all believers in many things.   As a matter of fact, we believe in things as fact which are not fact simply because we chose to believe them.   

This is the reason for so much deception and delusion.   

On the other hand experts are considered such because they know their subject area.   

Faith is usually associated with believing implying that it is not based strictly on knowledge.   

When we try to go from faith and believing to knowing (gnostic) what is required?   The Truth.   

Jesus did not come to start yet another religion in which there are adherents who choose to believe in that religion.   

Jesus is the Truth and came to reveal that Truth so that we Know The Truth and are made free by it.   

Jesus Is Truth does not mean that by being acquainted with Jesus - knowing some basic facts about Him - that we Know The Truth.   

To Know The Truth implies that one has considered the Truth and become totally convinced of it such that you no longer just believe the Truth in your mind but fully believe the Truth in your heart.   

How does such conviction come about?   
   ➛ hearing the Truth
   ➛ believing the Truth
   ➛ receiving the Truth
   ➛ revelation of the Truth

We understand that the Gospel is what we hear, believe and receive bringing salvation.   But what is this 'revelation of the Truth'?   

The Holy Spirit Of Christ Jesus is the Spirit Of Truth.   

When the Holy Spirit confirms the Truth that one has heard, believed and received, then we Know The Truth not just in a strong conviction of the Truth but in intimacy with the Truth.   

So to be a Christian Gnostic one must move from believing the Truth to knowing the Truth.   That movement is not possible by our efforts alone.   It requires the power of the Holy Spirit Of Christ Jesus to take what we know in our minds and cause us to know it in our hearts.   

This is why Jesus commanded us to be Spirit Filled.   

Jesus said the Words He spoke and the works He did, were the Words and works of His Father - His Holy Spirit Father.   

When the early church fathers relegated Spirit Baptism to a passing phenomena it moved believers from knowing the Truth to believing what they called the truth.   

This explains the Catholic church, its rituals, chatechisms, forms and traditions.   

We cannot study the things of God and come to knowledge of them simply from our intellect and reasoning powers.   We need God Himself to instruct our minds and hearts.   

A Christian Gnostic does not have some external mystical revelation of truth.   Rather he is the result of the marriage of the Words Of Christ and the Holy Spirit Of Christ in his heart.