What is the source and summit of our faith?

The phrase "source and summit of the Christian life" refers to the Eucharist, and can be found in The Catechism of the Catholic Church, as well as the Vatican II document Lumen Gentium, no. 11. In paragraph 1324, The Catechism states

The Eucharist is "the source and summit of the Christian life." "The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch."

REFERENCES

Libreria Editrice Vaticana. Catechism of the Catholic Church, (Mahwah, NJ: Paulist Press, 1994).

Flannery, A. ed. The Basic Sixteen Documents - Vatican Council II - Constitutions, Decrees, Declarations, (Northport, NY: Costello Publishing Company, 1996).