When at Mass does Earth and Heaven meet?
The Church teaches that during Mass, the Earth and Heaven come together. This means that those who are on Earth, and those who have gone before us in Heaven, all join together mystically as one family, praising God with the angels (CCC-1090; CCC-1370; CCC-1404; CCC-1371; CCC-1372). This joining together is a preview on Earth of how we will be spending all eternity - in the praise and worship of God. This eternal praise is symbolized in the Sanctus: "Holy, Holy, Holy is the Lord God Almighty" (Revelation 4:8).
To understand more about the mystery of the Mass, listen to
The Lamb's Supper: The Mass and the Apocalypse.