What is a saint?

One of my colleagues at work, Dr. Steven Shippee, is preparing a catechetical talk on the saints. He has given me permission to share the following paragraph, which is the introduction to his talk. I think he expresses well and creatively the importance of the saints in understanding the Catholic faith.

[The saints] are not an appendix to Catholic faith, not something you can skip but still really understand the book of Catholicism.  They are not an ancient holdover as an odd list of names recited at the Mass. They are, rather, manifestations of Christ and the Holy Spirit and the essence and fruit of their work of salvation.  And so they are actually the living book of Catholicism; this is why we join with them in prayer at the Mass.