Recently I've been partaking in multiple discussions regarding the concept of free will on this site (for the curious, see here, here, here, here), mainly because of its relevance in the context of the free-will defense against the problem of evil, and through these exchanges I've noticed that the concept of character is very important for at least some of its proponents. To illustrate this, let me quote this answer:
The "missing link" here is character. God has free will, and is fully capable of being tempted and enticed to do evil, but consistently chooses to use that free will in benevolent and righteous ways.
Or this answer:
One attribute of perfect character is having free-will and always using it to choose not to sin. (Sin is defined as breaking God's law, choosing to go against God's will. But since one can't use free-will to go against one's own will, God is by definition incapable of sinning.)
If God created a being that is totally incapable of sinning it would by definition not have free-will (with respect to sin). And without free-will, it would not have perfect character. So God cannot create a being with free-will that is incapable of sinning.
Yet it is possible for a created being to have free-will and at the same time be incapable of sinning (i.e. to have this attribute of perfect character).
Perfect character is something that a created being must develop over time, by learning to choose not to sin. Eventually, choosing not to sin becomes part of one's nature, while choosing to sin becomes impossible.
Christians have free-will, but their purpose in life is to develop perfect characters that always freely choose not to sin. They can develop this God-like character, but by definition no one can be created with it.
Note: I'm not endorsing these answers. I'm just showing them as examples of Christians who believe in the existence of some kind of mysterious interaction between character (the main topic of this question) and (libertarian) free will.
Just to make sure we are on the same page, I understand (libertarian) free will as an agent's ability to choose otherwise, that is, having more than one course of action available to them, when making a choice at time t, given a fixed past up to t. Essentially, the rejection of causal determinism when it comes to a person's ability to make decisions. And I think most people usually mean the same thing when they talk about (libertarian) free will.
Yet, the concept of character still puzzles me. First of all, because I'm not aware of any definition of libertarian free will where character is an essential part of the definition. I see character as a rather foreign concept in this context. And so when people pull out the character card in discussions about free will, to me it sounds like they are mixing concepts in a handwavy fashion, without providing any rigorous definitions, without clarifying how the concepts are supposed to make sense together in the same sentence.
What is character?
Is there a rigorous definition of character in Christianity? Does character exist as a "thing" in the first place (i.e., what is the ontological status of character)? Does character have any measurable or detectable causal effects on reality? For example, does an agent's character influence said agent in a way that determines or narrows the range of options available to them when making a decision at time t, and if so, how?
And what is the relationship between an agent's character and the laws of physics? Is character nothing but an emergent property of the laws of physics, in the sense that the concept of character is a convenient high-level abstraction, but ultimately adds nothing new to what the laws of physics can already explain? Is a person's character nothing but the current state of the neural wiring of their brain? Is character nothing but brain chemistry? Or is character something beyond the laws of physics, not reducible to them, and different from free will at the same time?
And if character goes beyond the laws of physics, where is the information of this character stored? Can it change/be updated over time? Does it obey its own "character update rules"?
In short, is there a rigorous definition of character in Christianity, and how is this definition reconciled with the laws of physics, how the brain works, and how libertarian free will works?
Regarding my sub-question about the relationship between character and the laws of physics, this question is closely related: How do defenders of libertarian freewill reconcile it with constraints imposed by the laws of physics?