My answer: a saint or a Christian is like a sacrament. And, in Catholic circles, when we speak of the Sacrament we mean the Eucharist. And for Catholics and some other Christians, the Eucharist is none other than Jesus himself.
Hence, a saint or a Christian is like Jesus.
But let us go deeper (in Spanish, "profundizar"). The Eucharist is the new Passover. Jesus is the Passover lamb. The saint or Christian is like a Passover lamb at the heart of the pivotal Exodus experience which gives us the hermeneutical key to the entire Bible and to all of Christian theology.
What does the Passover lamb do for the people of Israel? It protected from death, it healed from the ravages of centuries of slavery, it liberated from that slavery. The same things that Jesus did on earth and that Jesus does today through the liturgical sacraments:
Protect, Heal, Liberate.
The conclusion: A saint or a Christian has the mission of protecting, healing, and liberating others because the saint or Christian is like a sacrament.
(Image by blogger; Summer 2013)