Council of Orange? Don't you mean the Council of Ephesus? The Orthodox didn't change their theology in the Council of Ephesus. They stated that which was always taught. Read the very words of the Council, which
For one, the issue of Antinomianism is the only logical result if there is no human cooperation required in salvation. That's just in the definition of the word Antinomian:
one who holds that under the gospel dispensation of grace the moral law is of no use or obligation because faith alone is necessary to salvation.
If faith alone is all that is needed, then a changed life is completely unnecessary to salvation. A person can do whatever he wants. He can go across the world raping, killing, torturing, blaspheming, and nothing will ever happen to his eternal soul as a result.
There is no argument that works of the law do not save, because the law does not go as far as Christ commanded us to go.
But following Christ's command is how we are saved. Christ did not say "you need do nothing but have a mental assent and I will save you". He used PISTIS. Pistis is not simple assent. It is not mental. In point of fact, the mental component of Pistis is the LEAST IMPORTANT PART. It has to be there, but the most important part is the action. It is not a noun. It is not passive. It is active and continuous. Christ did not say "believe once", because that wouldn't have even made grammatical sense in the Greek. He said believe ALWAYS. Another translation would be "be faithful to the Lord Jesus Christ and you will be saved". In John 3:16, it could be written, "For God so loved the world that He gave His only begotten Son, that whosoever is faithful to Him, will not perish, but have everlasting life". The problem is that most translations of the New Testament in the west were Protestant. They did the translating with the assumptions of the five solas coming BEFORE the meaning of the words themselves, which is why when we see the Syrian, Russian, and other translations which were done in the East, they do not use the passive present form. Let's observe some early prayers of the Church from St. John Chrystostom, much earlier than the Council of Orange:
1.
O Lord, deprive me not of Thy heavenly good things.
2.
O Lord, deliver me from the eternal torments.
3. O Lord, if I have sinned in mind or deed, forgive me.
4. O Lord, deliver me from all ignorance, forgetfulness, faintheartedness, and stony insensibility.
5. O Lord, deliver me from every temptation.
6. O Lord, enlighten my heart which evil desire hath darkened.
7. O Lord, as a man I have sinned, but do Thou, as the compassionate God, have mercy on me, seeing the infirmity of my soul.
8. O Lord, send Thy grace to my help, that I may glorify Thy holy name.
9. O Lord Jesus Christ, write me Thy servant in the Book of Life, and grant me a good end.
10. O Lord my God, even though I have done nothing good in Thy sight, yet grant me by Thy grace a good beginning.
11. O Lord, sprinkle into my heart the dew of Thy grace.
12. O Lord of heaven earth, remember me Thy sinful servant, shameful and unclean, in Thy Kingdom, Amen.
13. O Lord, accept me in penitence.
14. O Lord, forsake me not.
15. O Lord, lead me not into temptation.
16. O Lord, grant me good thoughts.
17. O Lord, grant me tears, and remembrance of death, and compunction.
18. O Lord, grant me the thought of confessing my sins.
19. O Lord, grant me humility, chastity, and obedience.
20. O Lord, grant me patience, courage, and meekness.
21. O Lord, implant in me the root of good, Thy fear in my heart.
22. O Lord, vouchsafe me to love Thee with all my soul and thoughts, and in all things to do Thy will.
23. O Lord, protect me from evil men, and demons, and passions, and from every other unseemly thing.
24. O Lord, Thou knowest that Thou doest as Thou wilt: Thy will be done also in me a sinner; for blessed art Thou unto the ages.
The first two prayers of this antiphonal prayer by St. John Chrystostom is to not be deprived of the heavenly good things and that God will not deliver him to eternal torment. Now, if he believed in OSAS, as you seem to imply in your posts, would John have asked this? Seriously. This is an evening prayer. Let's see some of his prayers from the pre-Communion prayers, just to ensure it wasn't a single instance:
O Lord my God, I know that I am not worthy nor sufficiently pleasing that Thou shouldst come under the roof of the house of my soul for it is entirely desolate and fallen in ruin and Thou wilt not find in me a place worthy to lay Thy head. But as Thou didst humble Thyself from on high for our sake, so now humble Thyself to my lowliness.
As Thou didst deign to lie in a cavern, in a manger of dumb beasts, so now deign to enter in to the manger of my beastly soul, and into my soiled body.
And as Thou didst not disdain to enter and to eat with sinners in the house of Simon the leper, so now be pleased to enter into the house of my soul, humble and leprous and sinful.
And as Thou didst not cast out the prostitute, the sinful woman who came to touch Thee, so have compassion on me a sinner who comes to touch Thee.
And As Thou didst not abhor the kiss of her sin-stained and unclean mouth, do not abhor my mouth, worse stained and more unclean than hers, nor my stained and shamed and unclean lips, nor my still more impure tongue.
But let the fiery coal of Thy most pure Body and Thy most precious Blood bring me sanctification, enlightenment and strengthening of my lowly soul and body, relief from the burden of my many transgressions, protection against every action of the devil, repulsion and victory over my wicked and evil habits, mortification of my passions, accomplishment of Thy commandments, increase of Thy divine grace, and inheritance of Thy kingdom.
For I do not come to Thee in presumption, O Christ my God, but made bold by Thine unspeakable goodness, lest I stray far away from Thy flock, O Master, and become caught by the wolf of souls.
Therefore I pray Thee, O Master, for Thou alone art holy, sanctify my soul and body, my mind and heart, my muscles and bones. Renew me entirely. Implant Thy fear in my fleshly members and let Thy sanctification never be removed from me.
Be my helper and defender, guide my life in peace and make me worthy to stand at Thy right hand with all Thy saints.
By the prayers and supplications of Thy most pure Mother, of Thy spiritual servants, the most pure angelic powers, and of all the saints who from all ages have been well-pleasing to Thee. Amen.
So again, "enter my soul" and "Let Thy sanctification never be removed from me". If he believed in Eternal Security, then he would have no reason to pray this. These are from the fourth century. This is much earlier than your Council of Orange.
As soteriology goes, the Council of Orange did not argue against the Synergistic view. And neither was it universally accepted, as evidenced by the fact that it isn't considered and Ecumenical Council, unlike the position of Ephesus from more than a century before. Welcome to history class.
The fact is that with Eternal Security, Sanctification is unnecessary. It's just decoration. There is no need to make the vessel itself clean. Just sweep the dirt under the rug and make the rug look nice and clean. Don't worry about the mildew and stuff eating away at the wood under the rug. That is Eternal Security, in a nutshell. It's why I left the Baptist Church in the first place. They were too busy making "there's a new name written down in pencil" jokes to get about the real business of Christianity: "acquire the Spirit of Peace, and thousands around you will be saved."