Are there any biblical references that verufy the teaching of Mortal Sin?
1 John 5:16 is arguably the sin of final impenitence and complete apostasy from the truth: this is what the Douay Rheims suggests in its commentary.
Are there any other Biblical verses to support the view of Mortal Sin?
Yes, there are. One of the best is James 1:14-15 – “Each person is tempted when he is lured and enticed by his own desire. / Then desire when it has conceived gives birth to sin; and sin when it is full-grown brings forth death.”
“Full-grown [sin] brings forth death,” but not “smaller” sin. That proves that there are “smaller” sins and “greater” sins. “Mortal” sins and “venial” sins. Mortal or “full-grown” sins will kill your spiritual life, but “smaller” sins won’t.
Another good one is Galatians 5:19-21 – “Now the works of the flesh are plain: fornication, impurity, licentiousness, / idolatry, sorcery, enmity, strife, jealousy, anger, selfishness, dissension, party spirit, / envy, drunkenness, carousing, and the like. I warn you, as I warned you before, that those who do such things shall not inherit the kingdom of God.”
And I wouldn’t discount 1 John 5:16-17 either. If final impenitence excludes you from heaven, well, that’s 1 mortal sin at least. But there is no proof that it is referring to the sin of final impenitence alone. We can just as well say that the term “mortal sin” in that passage refers to the KIND of sins that exclude you from heaven, and I think that explains the text better than the theory that it refers to the sin of final impenitence alone.
Anyway, I hope that helps. God bless!
-Dan Marcum