It's not presumption anyway. It's fact.
Ephesians 2:4-10 But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved—and raised us up with him and seated us with him in the heavenly places in Christ Jesus , so that in the coming ages he might show the immeasurable riches of his grace in kindness toward us in Christ Jesus.
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.
Being seated with Christ in the heavenly places is part of the redemption that believers now have and operate in now. It's a present reality, happening now in the spiritual realm in which we operate.
Do Catholics really think it's presumptuous to have confidence in God and His word when we simply believe what He told us?
I don't know about you, but we call it *faith*.
Hebrews 11:6 And without faith it is impossible to please him, for whoever would draw near to God must believe that he exists and that he rewards those who seek him.
Perhaps you don't mind telling others that God didn't or doesn't really mean what He promised us in Scripture, but count me out. I'm not going there.
You asked for scriptural references; here they are:
In Matthew 24:13 we are told that those who persevere to the end will be saved – a clear refutation of the notion of eternal assurance. Romans 11:22 speaks on a similar theme. In Philippians 2:12 we are told to “work out your salvation with fear and trembling” - not only does this refute the idea that works are of no avail, but also shows – when read in the context of the whole passage – that the idea of eternal assurance is foolish.
I Corinthians contains two particular passages – 9:27 and 10:11-12 which speak very clearly on this subject. In fact, I Corinthians 10:11-12 refutes eternal assurance explicitly – saying that those who think they are secure may fail! II Timothy 2:11-13 says that we must “hold out to the end” in order to be saved.
There are also passages which speak specifically about those who have received Christ and have then fallen away. Galatians 5:4, Hebrews 6:4-6 and 10:26-27 refer to people who are Christians (and, therefore, saved) but then commit sins and, while remaining Christians, are not likely to inherit Heaven.
Additionally, if we were forgiven all sins, past, present, and future, it would make no sense for Christ to require us to pray, “And forgive us our debts, as we also have forgiven our debtors,” which he explained is required because “if you forgive men their trespasses, your heavenly Father also will forgive you; but if you do not forgive men their trespasses, neither will your Father forgive your trespasses” (Matthew 6:12-15).
The illogic of eternal assurance
Eternal assurance is an illogical position for the same reason that sola fides is illogical – it denies free will and the very existence of sin. If one is eternally assured of salvation after stepping into some “group” of the saved, then what does it matter if we sin? It in fact means that sin does not exist – there are no moral absolutes and there is nothing that will offend God. This means we cannot choose God, and hence do not have free will. If there is no sin and we have no ability to choose sin or God, what need do we have for a savior? Eternal assurance in fact denies the very purpose for Christ’s incarnation.
The sin of presumption
The sin of presumption is the name given to the belief in eternal assurance; it is presuming on God’s mercy. It is not just a theologically incorrect position to hold, but is also one which is a sin because it makes one proud and think that one has no need of God’s further assistance. The person thinks they are already permanently “saved” and so they do not need God, the Church or anything else.