" But at the same time, Baptism is only good until the next mortal sin, at which point they are again "out of Christ". "
This is what the Fathers taught. +Symeon the New Theolgian put it this way:
"Baptism does not take away our free will or freedom of choice, but gives us the freedom no longer to be tyrannized by the devil unless we choose to be. After baptism it is in our power either to persist willingly in the practice of the commandments of Christ, into Whom we were baptized, and to advance in the path of His ordinances, or to deviate from this straight way and to fall again into the hands of our enemy, the devil."
I enjoy St. Symeon. His mix of praxis and theology is very well done. He certainly deserves to be ranked with the "Theologian"...
Regards