If Gnostic ideas are "essentially apostate" and "heretical", the question of their necessary and actual origin in Paul, for example, is simply being begged

The Gnostic heresy’s political successors :

First, they are all essentially apostate projects, enterprises that have arisen in the midst of Christian civilization with the aim of supplanting it.  And they could have arisen only within the Christian context, because, second, these projects are all heretical in the broad sense of that term.  That is to say, they are all founded on some idea inherited from Christianity (the dignity of the individual, human equality, a law-governed universe, a final consummation, etc.) but removed from the theological framework that originally gave it meaning, and radically distorted in the process. ... the key marks of the Gnostic mindset – the positing of unseen malign forces, the hermeneutics of suspicion and “dream world” theorizing, Manicheanism and shrill intolerance of all dissenters, even something like an immanentized eschaton (“The Storm”). 

For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places. -- Ephesians 6:12

Howbeit we speak wisdom among them that are perfect: yet not the wisdom of this world, nor of the princes of this world, that come to nought: But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory: Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory. But as it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him. But God hath revealed them unto us by his Spirit: for the Spirit searcheth all things, yea, the deep things of God. For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God. Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God. Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual. But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned. But he that is spiritual judgeth all things, yet he himself is judged of no man. For who hath known the mind of the Lord, that he may instruct him? But we have the mind of Christ. -- I Corinthians 2:6ff. 

Be not ye therefore partakers with them. For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light: ... And have no fellowship with the unfruitful works of darkness, but rather reprove them. ... Wherefore he saith, Awake thou that sleepest, and arise from the dead, and Christ shall give thee light.  -- Ephesians 5:7f.,11,14

Giving thanks unto the Father, which hath made us meet to be partakers of the inheritance of the saints in light: Who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son:  -- Colossians 1:12f.

Kami Nelson of the Wayne Dupree Show thinks slavery is inconsistent with the God of the Bible, who doesn't change

Slaves, be obedient to those who are your earthly masters, with fear and trembling, in singleness of heart, as to Christ; -- Ephesians 6:5

Slaves, obey in everything those who are your earthly masters, not with eyeservice, as men-pleasers, but in singleness of heart, fearing the Lord. -- Colossians 3:22

Who Rules The World, The Lord Or The Devil?

"He raises up the poor from the dust; he lifts the needy from the ash heap, to make them sit with princes and inherit a seat of honor. For the pillars of the earth are the LORD'S, and on them he has set the world."

-- 1 Samuel 2:8

"The earth is the LORD'S, and the fulness thereof; the world, and they that dwell therein."

-- Psalm 24:1

"Hear, O my people, and I will speak; O Israel, and I will testify against thee: I am God, even thy God. ... If I were hungry, I would not tell thee: for the world is mine, and the fulness thereof."

-- Psalm 50:7, 12

"The heavens are thine, the earth also is thine: as for the world and the fulness thereof, thou hast founded them."

-- Psalm 89:11

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"Now is the judgment of this world: now shall the prince of this world be cast out."

-- John 12:31

"I will no longer talk much with you, for the ruler of this world is coming. He has no power over me."

-- John 14:30

"[T]he ruler of this world is judged."

-- John 16:11

"For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places."

-- Ephesians 6:12