This is a question that nearly all Christians are confronted-with over the years (unless they are capable of deceiving themselves abut their own cumulative goodness!): if they are living as Cristians, then why aren't they becoming better and better people?
The answer (which I mostly got from reading William Arkle) is that Life is not designed to make us better people, but instead life should be seen as a kind of ideal School or College that aims to provide us with experiences from which we can learn.
Life is at root about experience, and learning from experience.
The benefits of this learning are primarily intended for our lives after death in the immortal resurrected Life to come; the benefits of Life are not (in essence) required for this temporary mortal incarnated life.
I'm certainly not saying that this mortal life is un-important, but trying to say in what ways this life is mainly important: the idea is that it is important in terms of learning knowledge by experience - not in terms of improving us in this life.
Life very obviously seems to be set up in this way. Life provides experiences which are challenges, sometimes repeated experiences of the same kind of challenges; and our job it to learn from these experiences (given that learning is very difficult, which is why that repetition is so often needed in order that genuine learning can occur.
(All good colleges know this: to build a skill (which is a practical form of knowledge) requires drill, multiple repetitions, frequent practice.)
If life is like an ideal form of college, then we should expect the same kind of results; and not expect what a college cannot provide.
For example, studying theology at college does not make someone a better Christian; but it can and should make them more knowledgeable about what a Christian actually is, what a Christian ought to do, the history of Christianity and so forth.
Conversely - some (many?) of the best Christians, the most advanced in Christianity; are 'naturally' so - naturally good, virtuous people; yet their understanding of Christianity may be defective and partial. Indeed the best Christians - qua Christian - are sometimes children, simple-minded and ignorant people.
It seems that the Christian life is not very effective at making better Christians! But that seems to be part of the plan. The Christian life may be very effective at doing what it is meant to do; and even more so when we recognise that our specific personal needs differ - so that Life may be bringing us to confront (and overcome) challenges of the kind we need most - and these challenges may be repeated, because that is the way (often the only way) we will learn fully to overcome that type of challenge.
By such an understanding, combined with our knowledge that this world was created by our loving Father for his children's benefit; we can infer the purpose of our mortal world and can also make a reasonable guess at our own needs, hence our weaknesses.
We can - to some extent and given the assumptions as premises - infer function from results.
For example, in my life I have for some decades experienced almost continuous problems and challenges related to illnesses of various types. If it is assumed that my life is, at some deep level, not a random accident but instead 'the life I need' (because if not, then God did not do a good job - which possibility is ruled-out by my assumptions); then this may mean that I am supposed to be learning how to live in the context of such experiences of illness.
Such experiences may not make me a better person in this mortal life - indeed, they do not seem to be having that effect! - but nonetheless these experiences may provide me with practical, lived knowledge ('skills') which I do need for my post-mortal existence, and which mortal life uniquely provides.
In a more general way - the basic nature of mortal life may be doing something similar. Unless God-the-creator is supposed to be incompetent or un-loving- it must be that actual human Life provides what we need (overall).
So, we should be able to infer what we need from what a 'Christian Life' actually, typically, achieves - on the basis that what is achieved will (in a world well-designed by a loving God) tend to match-up with what is required; and what is required reflects what God most wants for us to learn during mortal incarnate Life.
Note: The above scheme is made possible by the effectuality of repentance - which was made possible through the work of Christ. What this means is that we can live a life of multiple, repeated failures to attain The Good, yet so long as these failures are repented (and the ideal proper behaviour acknowledged) we will still attain salvation.