I think the crux of DEH lies in "Words Fail":
I guess I thought I could be part of this
I never had this kind of thing before
I never had that perfect girl
Who somehow could see the good part of me
I never had the dad who stuck it out
No corny jokes or baseball gloves
No mom who just was there
'Cause mom was all that she had to be
That's not a worthy explanation
I know there is none
Nothing can make sense of all these things I've done
Words fail, words fail
There's nothing I can say
Except sometimes, you see everything you wanted
And sometimes, you see everything you wish you had
And it's right there, right there, right there
In front of you
And you want to believe it's true
So you... make it true
And you think maybe everybody wants it
And needs it... a little bit... too
This is really the first time that Evan admits the truth to both the Murphys and himself: that he intentionally took advantage of a horrible situation to make himself "belong", justifying to himself that his actions were appropriate because he was "helping the Murphys".
Building on this is the recurring theme of sun, which represents truth, love, acceptance, etc.
From "Waving Through the Window":
Step out, step out of the sun
If you keep getting burned
Step out, step out of the sun
Because you've learned, because you've learned
Here Evan tells himself the lie that stepping out in the sun will only get himself burned, perpetually leaving himself "waving through the window". However, upon Connor's death, Evan feels he can create (i.e., lie about) a life that will bring him into the sun.
From "For Forever":
All we see is light for forever
'Cause the sun shines bright for forever
Life will be alright for forever this way
Two friends on a perfect day
And there he goes
Racing toward the tallest tree
From far across the yellow field I hear him calling "follow me"
And there we go
Wondering how the world might look from up so high
One foot after the other
One branch then to another
I climb higher and higher
I climb until the entire
Sun shines on my face
"Words Fail" is a turning point for Evan; he realizes that the sun he was creating through his lie is not true light (i.e., truth):
'Cause what if everyone saw?
What if everyone knew?
Would they like what they saw?
Or would they hate it too?
Will I just keep on running away from what's true?
All I ever do is run
So how do I step in
Step into the sun?
Step into the sun
In the end, Evan learns that being himself is enough and that seeking out a sun of his own making is never truly going to bring him joy:
EVAN (spoken)
Dear Evan Hansen,?
Today is going to be a good day. And here's why: because today, today at least you're you and—that's enough.?
COMPANY (sung)
All we see is sky for forever
We let the world pass by for forever
Feels like we could go on for forever this way
This way
All we see is light
Watch the sun burn bright
We could be alright for forever
This way
All we see is sky for forever
EVAN
All I see is sky for forever?
Evan's repetition of the company's line is what hammers the point home here. These lyrics are, of course, a neat juxtaposition of those used in "For Forever" -- the same lyrics with completely different meanings.
Overall, I found the messages of seeing oneself as enough (and the dangers of creating a lie of a life that you think will make you happy in order to feel "enough" ) to be wonderfully lyrical and immensely moving. Moreover, the integration of social media is incredibly apt, as it illustrates a person's ability, especially in this day and age, to mobilize, feed, and be reaffirmed by a movement that one creates (in this case, The Connor Project) and the way that social media has a life of its own that reacts to circumstances swiftly and unabashedly, regardless of truth (e.g., the high praise for Evan and the nasty tear-downs of the Murphys).
I absolutely disagree with the argument that the musical justifies Evan's actions because they eventually helped the Murphys cope with their grief. I believe Evan already hit rock bottom and learned to forgive himself prior to meeting with Zoe in the final scene. Moreover, Evan knows well enough that the Murphys could easily have exposed him, yet they chose not to. They also chose to seek healing amongst the horrible things that happened to them. It gave the Murphys agency, and they used that agency to show Evan grace and love.
My only gripe with the musical -- and I believe there's not really anything the musical's creators could have done about it -- is that most of the songs are hard to take at face value in the context of the narrative. "Sincerely, Me" is hilarious, but also totally not in the context of the narrative. "If I Could Tell Her" and "Only Us" are beautiful but also creepily emotionally manipulative (again, in the context of the narrative). "You Will Be Found" is an inspiring piece but also (once again, in the context of the narrative) falsely inspiring because it's based on a lie. I saw a highly-"liked" YouTube comment on "You Will Be Found" that claims the (spoken) lyric of "I know someone who really needed to hear this today, so thank you Evan Hansen", was incredibly powerful. Yet, this lyric is immensely ironic in context. (It's also immensely ironic how well-"liked" this comment was on YouTube.)
Then again, I felt the same way about "Let It Go" from Frozen. While most people find the song inspiring, I can only see it in the context of the narrative, which is Elsa saying, "Screw you, I can do whatever I want to this kingdom -- including FREEZING IT OVER -- because everyone has stopped me from using my special powers before. BUT NO MORE. Just you watch me..."