Bishop Faustus is referring to the fact that through Christ's passion we are given new life, and that the establishment of Christ's Church fulfils the covenant.
"Philippians 2:13 ....for it is God who works in you, both to will and to work for his good pleasure."
That is exactly what I just said.
When someone is born again, they become the church, part of the body of Christ.
Salvation does not come through it. It comes by salvation.