What is the basis for the belief "It is possible to have free-will and be incapable of sinning, but it is not possible to be created in that state"?

Bible (NKJV):

1. The saved will be perfect:

Therefore you shall be perfect, just as your Father in heaven is perfect.
— Matthew 5:48

I in them, and You in Me; that they may be made perfect in one, and that the world may know that You have sent Me, and have loved them as You have loved Me.
— John 17:23

But above all these things put on love, which is the bond of perfection.
— Colossians 3:14

But let patience have its perfect work, that you may be perfect and complete, lacking nothing.
— James 1:4

2. They will learn to become like God:

A disciple is not above his teacher, but everyone who is perfectly trained will be like his teacher.
— Luke 6:40

till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ
— Ephesians 4:13
(NLT has "… we will be mature in the Lord, measuring up to the full and complete standard of Christ".)

3. Perfection requires time and effort to develop:

… we also glory in tribulations, knowing that tribulation produces perseverance; and perseverance, character; and character, hope.
— Romans 5:3,4

do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
— Romans 12:2

Not that I have already attained, or am already perfected; but I press on, that I may lay hold of that for which Christ Jesus has also laid hold of me.
— Philippians 3:12

… always laboring fervently for you in prayers, that you may stand perfect and complete in all the will of God.
— Colossians 4:12

… perfect what is lacking in your faith
— 1 Thessalonians 3:10

… let us go on to perfection …
— Hebrews 6:1

But may the God of all grace, who called us to His eternal glory by Christ Jesus, after you have suffered a while, perfect, establish, strengthen, and settle you.
— 1 Peter 5:10

Therefore, having these promises, beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
— 2 Corinthians 7:1 — ?

4. Perfection will become permanent:

But when that which is perfect has come, then that which is in part will be done away.
— 1 Corinthians 13:10

5. Sin is the breaking of God's law:

… sin is the transgression of the law
— 1 John 3:4 (KJV) —

6. God and his Law do not change:

For I am the LORD, I do not change …
— Malachi 3:6 —

Jesus Christ is the same yesterday, today, and forever.
— Hebrews 13:8 —

The law of the LORD is perfect, converting the soul …
— Psalm 19:7 —

Do not think that I came to destroy the Law or the Prophets
— Matthew 5:17 —

7. God uses his holy spirit to communicate with fully baptized and converted Christians:

… walking in the fear of the Lord and in the comfort of the Holy Spirit …
— Acts 9:31

But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, …
— John 14:26

For the Holy Spirit will teach you in that very hour what you ought to say
— Luke 12:12

… not in words which man's wisdom teaches but which the Holy Spirit teaches, …
— 1 Corinthians 2:13

Facts:

1. There are things that even an omnipotent God cannot do.

• God cannot create a four-sided triangle; if something has four sides, it is by definition not a triangle.

Postulates:

1. Sin means choosing to go against God's will.

2. God has perfect character.

3. Attributes of perfect character include:

• Having free-will (in particular, the ability to choose not to sin).
• Never choosing to sin.

Lemmas:

1. The Law represents God's will.

• Sin is breaking the Law. (B5)
• Sin means choosing to go against God's will. (P1)
• Therefore the Law represents God's will.

2. God is intrinsically incapable of sin.

• Sin is choosing to go against God's will. (P1)
• By definition, one cannot, by free-will, choose to go against one's own will.
• Therefore God cannot choose to go against his own will. (F1)
• Therefore God cannot choose to sin.
• Therefore God cannot sin.
• (Note that this is not like Nixon's "When the president does it, that means it’s not illegal.", as God's Law does not change. (B6,L1))

3. A being cannot be created both having free-will and being unable to sin.

• Free-will allows one to choose whether to sin. (P3)
• By definition, someone that is unable to sin cannot choose whether to sin.
• Therefore no being can be created with both free-will and an inability to sin.

4. Being incapable of sin is indistinguishable from having a character that never chooses to sin.

• One's behaviour is identical in both cases.
• People may believe they are incapable when actually they aren't.
• People may believe they are capable when actually they aren't.
• Whether by choice or not, and regardless of their belief, they will not sin.

Thesis 1: It is possible to have free-will and be incapable of sinning, but it is not possible to be created in that state.

• The first half is true for at least one being: God has free-will (P2 and P3), and God is incapable of sin (L2).
• The second half is true: "A being cannot be created both having free-will and being unable to sin." (L3).

Thesis 2: A being created with free-will can develop a character that is incapable of sinning:

• One goal of a Christian is to attain perfection by accepting the training of God's holy spirit to change one's mind to have a perfect character that matches the will of God. (B1, B2)
• Developing a perfect character, one that will never choose to sin, requires time, effort, and assistance (B3, B7):
  • Knowing whether something is a bad choice will become easier.
  • Choosing to go against God's will will occur less and less frequently.
  • The attraction of various sins will lessen.
  • The attraction of sins will turn to repulsion.
  • Choosing not to sin will become habitual and natural.
  • Eventually one will never be tempted by any sin, and will never choose to go against God's will. (B4)
  • One will effectively become incapable of sin (L4).

You seem to have put a lot of thought into this question and there is a lot of backstory. I don't have the time for a full breakdown of every issue, but I will attempt to clear some of the weeds away for you and other readers by addressing some unhelpful assumptions, before offering an answer to your question.

Faulty assumptions:

1. A libertarian sinless maturity erases the logical possibility of sin.

The title of your post asks 'libertarians' like myself to defend the idea that men and women in heaven will be "incapable" of sinning. You take this word from a post other than my own, and so I reserve the right to distinguish it from my own view. My explanation is that a fully mature Christian, filled with the Spirit, fully united to Christ and his body, "would" not sin, not they "could" not logically sin. I point this out at the bottom of the quote you take from my earlier responses to similar questions.

Many things are logically 'possible' while in every other sense being impossible. It is logically possible for a cancerous tumor to grow me a working third arm but I can state with certainty that this will not happen. This will not happen both because it is not within human DNA (genetic 'character') for humans to have a third, working arm, and because it is within the nature of cancer to produce only cancerous, not fully functioning, growths.

Logic is only one domain of knowledge, I am not entirely convinced that it perfectly maps to our reality (or at least our perception of it), and it is not the basis of my claims that Spirit-filled Christians will be "fully mature" in heaven (Col. 1:28, NIV). To take Nicodemus out of context, is a child, fully grown, able to enter into his mother's womb and be born a second time? No! But this is not a matter of logic, but a matter of maturity. And in the same way, is someone who, in the resurrection, be perfected by love able to sin again? Can light coexist with darkness? No!

Read what Paul writes about our resurrection moral character in 1 Cor. 13: 10-13. Many translations use the word "perfect" in place of "completeness".

"...but when completeness comes, what is in part disappears. When I was a child, I talked like a child, I thought like a child, I reasoned like a child. When I became a man, I put the ways of childhood behind me. For now we see only a reflection as in a mirror; then we shall see face to face. Now I know in part; then I shall know fully, even as I am fully known. And now these three remain: faith, hope and love. But the greatest of these is love."

2. God's free-will is analogous to our own.

Another faulty assumption you make is that the concept of free-will applies perfectly to both God and temporal creatures. Even your use of "uncreated" is a bit sloppy since it has confusing connotations compared to classical language like "eternal". "Not created" is a better phrase since to uncreate something is to destroy it and that is the exact opposite of what is meant when we say that God is eternal.

There is less, but still similar slippage when we uncritically assume that God's nature/character is capable of being described like we would a ball. When we look at a ball and see that it is round, the adjective "round" has meaning because we can compare it to other balls and round objects. But we would not say it is roundness, merely that a structural/spatial concept within our minds (roundness) generally describes one aspect of the ball. Our brain forms this spatial/linguistic concept through exposure to roundness in many objects as an infant in combination with words like round, circle, etc. Except for Neo-Platonists, there is not "roundness" in the world apart from its concrete expressions in relation to abstract concepts and words in our brains.

The nature and character of God is incomparable because he is incomparable. There is one God. And oneness is part of the nature of God. This is fundamentally different than anything else. So descriptions of him must come from him through revelation, and even when they are revealed, they are univocal. Through revelation, we are able to know things about God, but we can never know them in the same sense as we know things about creation, because he is fundamentally incomparable to creation. Un-createdness, if it does describe God, is univocal and beyond logical analysis without an analogy in creation. Since God is the only 'un-created' being, we can develop no concept of 'un-createdness" except as it appears ineffably in God.

So, when you assume that "free-will" is a single concept that merely applies differently to God and humans, you are starting off on the wrong foot entirely. Free will is only a word invented by philosophy to describe the genuine choices which God seems to present humans with in scripture. Choices which logically permit us to choose one or another thing, which have temporal consequences. God is fundamentally "free" in the sense that nothing limits him, in any way or direction, except himself. God's freedom is of a fundamentally different order than human free will. We call the ways that he limits himself, his nature or character. But even the word character is here fundamentally different when predicated of God than when predicated of creatures. Humans have limited, moral choices, where the ability to do or not do something is described as freedom. God is unlimited temporally - as an eternal being he cannot mature over time but is forever perfect. Choice is temporal, concept - an eternal being has no counterfactuals. For humans, moral goodness is judged against Christ, the ideal human because he perfectly reflects God's character as it is revealed in creation. Christ did not sin, because he was fully submitted to the Spirit through whom the triune God works to keep his children from sin.

An attempt at an answer:

With these clarifications out of the way, I can finally attempt an answer to some of your questions. Note: those who do not subscribe to the 'classical' perfect being theology may disagree with much of what I say.

"What is the rationale behind this dual perspective on (libertarian) free will, which posits that created beings necessitate maturation over time while uncreated beings do not require any such process?"

There is no dual perspective because free-will is a concept that applies only to creatures. It seems to reflect some aspect of God's freedom but God does not need to make choices because he is not temporal. Uncreated is an unhelpful term.

"Does it derive from sacred scripture or from deeper philosophical reasoning?"

Many ancient peoples did not believe in free will, and apart from theological reasons, many today don't as well. Non-Judeo-Christian faiths are often deterministic and fatalistic. Contrast this to the responsibility to choose right and not choose wrong displayed throughout scripture, such as Romans 7 and Joshua 14, and free will is a Christian concept. But is it a biblical concept? The term is not used in scripture, it is not logically defined, and is thus a valuable, and Christian philosophical construction.

I don't have time for research into sources for these questions: "Is this view widely held within Christianity? Can we trace its origins back to ancient Christian thinkers? Are there any historical Christian sources that explicitly and unambiguously support this view?" Here is a good book from a scholar dedicated to the ancient and classical Christian sources who generally comes to argue for libertarianism.

You close by asking for a logical argument. But I cannot compare it to God's 'free-will' since that is not a predicate of God. Furthermore, I don't think the problem is fundamentally a logical one. The problem is time, what does it mean for creatures, unlike God, to exist only in and across time? What does freedom mean within that inherent, creaturely limitation? Libertarian's define free-will in terms of logical possibility, but the moral choice runs deeper than the logic. It depends on the character of the person - are they slaves to sin or filled with the Spirit? The other problem is, I'm not a logician ;).

Hope this helps.