Yes the song rhymes in various verses and choruses but when I listen to the song I tend to focus more on the rhythm and how the lyrics connect to that verses the actual sound. In the choruses, pre-choruses, and bridge the rhythm of the song is very syncopated and follows a pattern of "short, long, short, long" and other variations of the two different lengths of the lyrics the singer sings in one breath. Here is an example or the pre-chorus to chorus area of the song:
Pre-Chorus: You swore and said
Though I've never been through hell like that
I've closed enough windows
TO know you can never look back
Chorus: If you're lost and alone
Or you're sinking like a stone
May your past be the sound
Of your feet upon the ground
So first there is a pattern of "long - short - long - short - long" followed by three long lines and there there is the steady beat for two lines and then the short and smooth "carry on" in the chorus. This rhythm stands out to me because it seems to me like the song is an actual like journey, a road someone is traveling along. It seems to be steady and easy to follow along the "long" parts but every so often you hit a "short" bump. But as the song's title explains, the singer is able to Carry On and make the best of it.
Another thing that I notice that I guess you could classify as theme of the song, is the wording and meaning of the pre-choruses as they change from beginning to end. At first, the pre-chorus gives a sense of struggle and acceptance, like the singer is saying they know their life is tough and they are the best of people, but they are Carrying On (see the pre-chorus above). But somewhere in the bridge the singer's purpose and sense of life changes and the final pre-chorus becomes a song about freedom almost. The basic lyrics are similar in wording but the meaning is completely different. The singer says "we are who we are" and realizes that no matter who he is and what life he has been given he is making the best of it and will carry on for miles and miles:
We are shining stars
We are invincible
We are who we are
On our darkest day
When we're miles away
So we'll come
We will find our way home