What is the sin of "presumption"?

This is my first post on here. I was prompted to post as I am a Protestant (former Catholic) who has been talking with a Catholic friend of mine. Protestants believe that one can know that they are saved and he says that Catholics don’t know. In fact I have read that it is supposed to be a sin (sin of presumption) to even say that you know you are going to heaven.

I don’t want to get into a big arguement about this…but he seems to claim that even Paul did not know that he was going to heaven. That sounds way off in light of scriptures that I read.

[size=2]At the end of Paul’s life he wrote to Timothy. 2 Tim 4:7-8. (New American Catholic Bible) "I have competed well; I have finished the race; I have kept the faith. From now on the crown of righteousness awaits me, which the Lord, the just judge, will award to me on that day, and not only to me, but to all who have longed for his appearance. "[/size]
If Christians can not know that they are going to heaven and have eternal life…then why does John say that you can know.
**[size=1][size=2]1 John 5:13.[/size]**I write these things to you so that you mayknow that you have eternal life, you who believe in the name of the Son of God.
John said that he wrote so that they could know.
I honestly don’t understand how Catholic think it is a sin to believe John when he says you can know.

Were John and Paul committing sin when saying that they know they have eternal life?

I am confused. Is this the official teaching of the Cathlic Church?

While we do not have an absolute assurance of salvation, we do have a moral assurance. That is, we are assured of salvation provided we die in a state of grace - free of unforgiven mortal sin. With this in mind we can understand the confidence with which Paul and John write.

Presumption is different. Presumption presumes salvation may be attained either (1) through one’s own abilities, or (2) through God without one’s own cooperation.

The Catechism of the Catholic Church (CCC) explains, “There are two kinds of presumption. Either man presumes upon his own capacities, (hoping to be able to save himself without help from on high), or he presumes upon God’s almighty power or his mercy (hoping to obtain his forgiveness without conversion and glory without merit)” (CCC 2092).

Recommended reading:[LIST]
*]Assurance of Salvation?
*]Christians Have No Guarantee of Heaven[/LIST]

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