kek
>mortal sin
Ah,
the Popish sin distinction.
The sin unto death is apostasy,
which is falling away from Christ to another Christ and another "gospel".
One will know the difference between the two by comparing one's belief to what the Prophets and Apostles taught,
in other words,
the Foundation upon which Christ's Congregation,
His body,
is built.
Holding to doctrines the Prophets and the Apostles never taught,
in lieu of only what they taught,
is the definition of apostasy.
That is the sin unto death.