Inside and Out Lyrics

Lyric discussion by AdamantVision 

Cover art for Inside and Out lyrics by Genesis

I understand how the first part of this song has to do with a guy's brother reading a letter to him and his mother, explaining his life for the past few years after having been thrown in jail on questionable charges. What I have always wondered is the significance of the instrumental part at the end. I know it doesn't have lyrics but the mood changes considerably and I've never been quite sure what it means compared to the rest of the song.