I for one would really like to read this book; this collection of letters. Putting aside what I think about publishing private letters … I think that reading what this father writes to his adult children, especially when writing to them about their doubts, could be hugely helpful to other parents struggling with the same issues.
Talking about faith with our grown children is such a potential minefield, especially if they are going through a phase of doubting or rebellion or naming real struggles that we might not want them to name. It can be immensely threatening to parents, and fraught with all kinds of emotions.
To be able to see how another parent deals with this in a winsome, grace-filled, honest way … well, I think it might be greatly encouraging to me in my journey as a parent of young adults who at times, question the faith of their youth.

A couple thoughts:
It seems most epistles contain some sort of fruit of the Spirit or take off, put on passage where we are to take off things like anger, sexual sin, bitterness, wrong speaking and put on things like kindness, respect, gentleness, forgiveness, thankfulness, self-control, love, joy, peace, etc. These are general ideas almost any reasonable person can agree to but the more you try to do it, the more you realize how hard it is to truly, deeply live this out in the face of injustice.
Thought 1: Most of us want this, we just can’t do it.
I love learning about and seeing pictures of ancient Egypt. Their culture involved learning, widsom, culture, architecture on such a grand scale for thousands of years. Cleopatra is closer in time to us than to the Old Kingdom. Some of their wisdom writings are copied in the biblical Proverbs. The ancient kingdoms are gone, now, only ruins to tell their story. I don’t fault the designers of their culture with this ruin – I fault those who came and destroyed artifacts, etc.
Thought 2: When we see kingdoms in ruin, we recognize that desctructive forces prevailed against what was something better.
These two thoughts mean something to me. They may not move others. I see the fall, the flood, Babel, Lot moving to Sodom, Abram using Hagar instead of waiting in faith, and so on and so on as examples of independance from God. God created the garden as a place of completely open trust and no shame. The more humans assert their independance from God, the worse we make things.
Conclusion: To be the people we know we should be requires God’s creation and resurrection power. The lives of those who are transformed by this power and respond in grace to those who mistreat them (something I know I am not capable of by myself) are examples of God intervening in this world with his creation and resurrection power.
I don’t know this daughter and her concerns may be completely missed by these comments. However, I emerged from my “Truman Christian” background with some deep internal questions and problems. For some reason these two thoughts, among others, speak to me. Perhaps just sharing my own heart and story would count for something. My son is only 10 and his heart is very open to God and the Bible. If he were to begin questioning, I would see if there is any part of my heart or story that might speak to him.
Perhaps what he would most need is a respectful hearing. I hope I would give him that if that is what he most needed.

Not good answers:
1. All doubt is sin.
2. You are being demonized.
3. Memorize more Bible verses.
I think creating space to listen and to love and to express on alarm or panic is the atmosphere in which the Spirit may do a good transformative work.

oops…comment #3 should read “no alarm…”

What would you tell your daughter (or son) if either of them expressed probing doubts about their faith?
This is a question that many of us who are Christians and parents will likely face at some point – or at least we will know that our kids are struggling even if they won’t talk with us. Doubts and questions are not exactly a new phenomenon. I’ve certainly had plenty of my own.
More than anything else I think that it is important to listen and acknowledge the questions as real and to carry on an honest eye-to-eye conversation. Erecting fences and boundaries isn’t likely to work on meaningful any level.

What would you tell your daughter (or son) if either of them expressed probing doubts about their faith?
I’d say, yeah, I have those doubts too. But in the end, I choose to believe in God. If I don’t have God to worship, I would end up worshiping myself all the time. And that wouldn’t be good.

The one thing I wouldn’t do is hit the roof or the panic button. I would calmly and rationally discuss their questions and doubts and not try to have all the pat answers. God is so much bigger than our doubts. Above all, I would entrust that child and all of their doubts and concerns to the Father. I would even encourage them through their doubt and unbelief to have a conversation with God about the issues. After all, if they are doubting His existence and He doesn’t answer, they have lost nothing.

Having not read the book, based on what you’re saying, I think if I were his daughter I would have found his answers very unsatisfactory.
But I have come to an understanding over the years that everyone’s faith has different foundations. And everyone’s doubts have different causes.
So it’s hard to suggest a one-size fits all solution to doubt. I think that’s where just talking and conversing about why you believe and you struggle with your own doubt probably does the most good — unless they have specific issues that you think you have ‘solutions’ for.

I will soon have a daughter. Although I am an Atheist, she shall not be. I am an Atheist because I was once religious, and am now without it. She’ll never be brainwashed into that cult from the beginning, and will (I hope) have no need to characterize herself by what she is not.
It is my understanding that the religious will be the minority before she leaves my home for college; if the trend from the last twenty years continues for another twenty.