Modern people feel guilty, but they do not repent - and if they do not repent, they cannot be Christian.
So, what blocks repentance?
People cannot repent until they know what they should do, and that they are not doing it; and they cannot know what they should do, until they know the structure of reality: the human condition.
If so, it is futile trying to get people to repent when they do not know the structure of reality, and if they deny even that reality even has a structure.
Most modern adults are alienated - cut off from reality - and this is experienced as negative emotions: misery, boredom, anger, anxiety, demotivation...
But they do not know what they are alienated from. Therefore nothing can be done about alienation - except distraction and intoxication to stop the feeling (but not the cause).
Modern people are stuck. They feel bad and they not only do not know why they feel bad, but they also deny that there is any objective reason for feeling bad except for illness and a repressive 'society' - therefore a religion which tells modern people to repent is interpreted as deliberately making people who already feel bad, feel even worse. Which seems like a very nasty thing to do.
So, what should be the first step in modern deep apologetics?
Whatever the first step in apologetics it will be incomplete, because it is the first step. Its main role is to provide what is necessary to back-reference when the further steps are added (IF things get even that far).
My present notion is that the first step should be to describe the basic set-up, the human condition and relation to God the Father and Jesus Christ - the story of the history of Man: where we came from and where we are going.
This story must be truthful, of course! - and must also be inspiring - if it is to be useful.
But the truthfulness of the very first brief outline must be carefully considered, in the sense that any brief outline must omit mention of difficulties that cannot be dealt with without interrupting the story: this is just common sense about how to teach.
In teaching something difficult, you first of all give the whole thing, stated clearly and didactically in plain language (minimal jargon) without qualifications or quibbles - and only then, once people have 'got' that simple version, you go back over the story adding nuances, discussing difficulties or ambiguities, teasing out implications etc.
The is what Christians need to do for the modern audience - each Christian denomination needs to reflect on this matter, and work on telling the story of Man and God for the first time: what to include as necessary for further building, what to leave-out as misleading, what to emphasize as interesting and inspiring.
If people understand the basic story of human life, they can then understand the nature of sin and why sin is (objectively) sin; because then they understand what they are sinning-against: only then can modern people repent.
Note: I recognized the need for this after reflecting on the content of the published manuals for Mormon missionaries - and the prominence given to The Plan of Salvation.
Here the LDS church sets out from its own perspective 'the basic story' of the human condition, God's relations with Man; describes it very clearly and in a way which is potentially both interesting and exciting/ inspiring. Once this basic story is understood, then more detailed discussions can be related back to it, and questions can be answered by reference to the overall Plan.
I think other Christian denominations ought to be able to generate a comparably brief, simple, clear, and inspiring account of the basic story of Man and God, from their own perspective.
Further note: I am not interested in publishing comments critical of the Mormon Missionary Manual, nor of Mormonism - I am referencing this manual as a good example of the kind of thing which is needed, and to make clear that most Christian denominations do not provide anything half so useful for apologetics.