Why theme lives between characters, not inside one
What a reader experiences is not a character but the space between two of them, so the same claim carried by three different pairs is what stops a theme sounding like one note.
How to build a supporting cast around your theme
The people around your protagonist do more than help or get in the way. Each one can show a different answer to the question your story is asking: someone who already lives the answer, someone who tempts your protagonist the other way, someone who doubts, and someone who took the other road.
When each of those positions is covered once, the cast feels full and your theme comes through without anyone giving a speech. When two characters cover the same ground, or a position is left empty, the cast feels thin no matter how colorful the characters are.
Every insight on this topic
Why one right choice at the end doesn't prove your theme
A protagonist's climactic choice on its own is consistent with your story's position without ever establishing it, because a second position would explain the same choice equally well.
How to show your theme without characters preaching
A position can be stated, embodied, or carried by what happens to somebody, and a cast can be fully staffed on the first and starved on the other two.