Prince Escalus pronounces these words almost at the close of the play. Romeo and Juliet have committed suicide. The prince is addressing the heads of the feuding Capulet and Montague households and he gives them a severe scolding. He tells them to witness what a plague their hatred for each other has brought to their families - it has brought terrible suffering which has now culminated in the deaths of their only children.
The prince tells the two families that their deep enmity and rancor has culminated in divine intervention. Since their feud has brought so much pain and upset the natural peace and calm of the beautiful Verona, God has found it necessary to intercede and bring an end to their wanton savagery. This interruption was most harsh and resulted in the deaths of their beloved offspring (their joy). It was the love that the two youngsters had for each other that brought about this tragedy since their relationship would have never received support from any of the families because of their irrational hatred for each other.
The prince is brutally direct in his address and obviously wants the two families to acknowledge and take responsibility for their actions and bring to an end their destructively malicious conflict.
In the end, the two households realise that their war is a futile and foolish exercise, for they have lost their most precious assets. They then decide to put a stop to the acrimony between them and make peace, as indicated in the following extract from the final scene:
O brother Montague, give me thy hand:
This is my daughter's jointure, for no more
Can I demand.
But I can give thee more:
For I will raise her statue in pure gold;
That while Verona by that name is known,
There shall no figure at such rate be set
As that of true and faithful Juliet.
As rich shall Romeo's by his lady's lie;
Poor sacrifices of our enmity!
The Prince says this in the very end of Act 5. He is talking to both Montague and the Capulets. He is telling them how wrong it is that they have been warring with each other for so long. He is reminding them that Heaven or God has now had to intervene and give them real consequences that will make them consider changing their behaviors. The consequence for each of them is the death of their children (their joy). Had they not been at war with each other, none of this ever would have happened. Ironically, their hate was defeated by love. The Prince pointed out that their joy in life was killed by love, Romeo and Juliet's love for each other which could not be quenched legally in front of their parents. The hiding that the kids had to do helped lead to these deaths.