While Act II is packed with a lengthy and intimate interaction between Romeo and Juliette, Act III is a little more straightforward and simple. It is an important moment because the couple gets married! This wedding scene is interesting because it is something that the librettists and Gounod created and added into the work. (In the Shakespeare play, the lovers are married off stage.) Gounod was a very religious man (more on this later!) and I think he wanted this scene to include some choral and sacred-inspired music. The way the music is set binds the lovers even closer together which symbolizes their union through marriage.
There is a nice balance to this act. It begins with Romeo and Friar Laurence, then Juliette joins and they are married. The rest of the act is a violent fight scene between the Capulets and Montagues. It is packed with action: Tybalt kills Mercutio, then Romeo kills Tybalt. There is such a juxtaposition between the happy and sacred marriage of the two young lovers and this violent fight scene where death occurs and Romeo is banished.
No. 10 – Friar Laurence, Romeo, and Juliette
Romeo and Friar are talking about how Romeo is in love again, but with Juliette. As she enters he sees her “La voici!”.. She responds “Romeo!” These two statements occur on the same pitches an octave apart. Again, we see Juliette matching Romeo’s musical material exactly. Romeo says “My soul called you!” I think this is a great example of how Romeo has this fateful pull on Juliette. He just thinks of her, and suddenly she appears!
“Voici mon époux!…“Je m’abandonne!” – She tells the Friar – “Here is my spouse!” Even though they aren’t even married yet, Juliette is fully committed to Romeo. She is proud of their love and isn’t afraid to abandon herself. At this moment, Juliette’s music is quite melodic and beautiful, but it is filled with accidentals and does not adhere to the written key signature. This represents her once melodic and tuneful self being broken down into something more chromatic and disjunct. Her disintegration culminates at the end of this phrase, “Ciel unissez-nous!” all on a repeated pitch. Again this musical motif of repeated pitches appears when Juliette is losing herself/her melodic style.
“La voici! … Romeo!” 
“Voici mon époux!”
No.11 – Wedding scene
Trio – Friar Laurence, Romeo, Juliette
This wedding scene is where we really witness the fusion of the two separate lovers into one. Every phrase they sing is in octaves with each other; this is a closer connection, harmonically and symbolically, than the sensual third harmonies in Acts I and II.
From this moment on in the opera, Juliette’s music begins to really morph. Her and Romeo are bound together by holy union and it’s shown in the way that Gounod sets their parts and how they interact. I will talk about this more in Act IV and V, but as the opera progresses, their vocal lines start to interact so closely that they are essentially the same voice. In Act V, they complete each other’s thoughts and musical phrases.
“Que ce couple chaste et fidele…” – This is Friar Laurence’s final line before Romeo and Juliette’s final vow. As he says “united in eternal life”, the music intensifies and is possibly the most dramatic and densely orchestrated moment of the entire scene. This intensity in the music foreshadows the fatal ending to come: they will be united in eternal life… but that eternal life will come much sooner than they anticipate.
“Seigneur! Sur notre amour daigne abaisser les yeux!” – Lord, to our love, deign to look down upon us!
This very last line is (SPOILER ALERT) almost exactly the same as the final words spoken by the lovers in Act V.
Quartet – The Nurse joins as they celebrate!
“O pur bonheur! O joie immense!/Oh pure happiness! Oh immense joy!” –This music is very arpeggiated, light, energetic, and obviously happy! This reminds me of the Juliette from Act I.
“Sois béni” – This line is joyful, but is foreshadowing later in Act V when the lovers sing this as they are dying.
“O pur bonheur!” 
“Sois béni!”
In this Act, it is amazing to see how Gounod juxtaposes the sacred and beautiful union and the devastating and violent murders.There are also many moments both musically and textually that foreshadow the fatal ending. Juliette becomes even more connected to Romeo and that is shown through their music; set always together and always in octaves with each other.