Q: In regard to mortal and venial sins seen in 1 John 5:16-17, I was recently discussing this a friend who is Lutheran. He pulls out his NIV Bible and he reads the same verse and instead of it saying "There is a such thing as deadly sin, about which I do not say you can pray", it says something to the effect of "There is a sin that leads to death, about which I do not say you can pray", in which case he says it is referring to the sin against the Holy Spirit talked about in Mark's gospel. Is this biblical justification for mortal and venial sins now moot for me against anyone who carries an NIV Bible?
A: First of all we have to keep in mind that without a distinction between mortal and venial sins, we cannot have a proper concept of the Original sin of Adam.
Now, if we follow the logic of the translators of the NIV, then we need to be consistent and would have to translate 1 Jn. 5:17 also in the singular to read "but there is a sin which is not mortal." Following this logic, we have two singular sins. One leads to death (mortal). One does not. If they say that the one mortal is blasphemy against the Holy Spirit, what do they claim is the one not-mortal sin? They would probably answer that it is absurd to say that there are only two possible sins, and they would be right. Hence the absurdity of their argument for the translation in the NIV and the absurdity of the logical conclusion that follows!
John 19:11 has Jesus say "...for this reason the one who handed me over to you had the greater sin." Jesus Himself makes a distinction in the degree of sins! We know that the "one who handed" Christ over was Judas. Judas certainly didn't blaspheme against the Holy Spirit. So how is it that he commits a greater sin? Because his sin is a mortal sin and Christ Himself makes a distinction between degrees of sin.
Also, Paul in 1 Cor. 6:9-11 states: "Do you not know that the unjust will not inherit the kingdom of God? Do not be deceived; neither fornicators nor idolaters..." If their were no distinction between sins, Paul's telling us of certain sins that cut us off from God (i.e. mortal) would be superfluous!