Rabbi Abba son of Kahana said, “David’s generation were all righteous, but because there were informers among them, they fell in battle...Ahab’s generation were idolaters, but because there were no informers, they went to battle and were victorious.”
Jerusalem Talmud, Peah 1:1.
Jerusalem is the city that joins all the tribes together as one. When the Jewish people come together as one, nothing can destroy Jerusalem. And only when there is love and caring between them is the destruction and our exile healed.
When a father sees his children working together with love, he is prepared to give them anything.
Yes, love for one another means also to care enough to encourage the other to do mitzvahs and learn Torah.
But first comes the love.

On a spiritual level, the city of Jerusalem is built within our hearts. When the hearts of the people connect with love, care, mercy and kindness between them, they are aligned with G_d's qualities. These connections form a divine structure that nobody can destroy. The 'bricks' of this holy 'city' are bonded with G_d's light between them. Spiritually, G_d's light flows between the hearts of the people in this this holy structure, The Ten Sefirot.
Let's build the city of Jerusalem in our hearts. A model city, a blueprint for all humanity. The Jewish people must be a light to humanity so all will be included in the peace of Jerusalem.