One interesting thing to look at in most of Paul's letters is how that in the first half of his letters he goes through and explains who you are as a believer and what happened to you at the cross. The second half is not as much a list of do's and don't's but instead a description of how it should be natural to act as a believer (when you're walking in the Spirit). But most believers still function in their old habits, not renewing their mind with the truth of who they are (Roma 12:1-2). So I absolutely agree with your son that most Christians struggle because they truly do not understand the grace that is already theirs.
Thank you, Ken! You articulated perfectly what has been jiggeting about in my mind... I especially like your description of the second half as "not as much a list of do's and don't's but instead a description of how it should be natural to act as a believer."