I'd rather be sure after the Judgment, not before.
As far as the silliness of "the sin of presumption", you completely misunderstand the Mosaic Covenant, the New Covenant, and Jesus' mission as Messiah.
Jesus came to take away the sin that separates us from eternal life with God the Father. Either He took it away by His sacrifice on the cross and His high priestly work or He did not. If He didn't, then He was a false prophet. If He did, then we now have eternal life through faith in Him. We are all born wicked; either we are righteous (and have therefore received the inheritance promised to the saints, eternal life) or we are not. And we are not made righteous by participating in the sacraments and doing good works (as noble as those things may be). We are only made righteous through the atoning blood of Jesus Christ, through which His righteousness is inputed to us.
The Old Covenant (i.e., Mosaic Covenant) was insufficient to take away sin. That is why the Old Covenant Jews did NOT have everlasting life apart from Messiah. That is why Jesus came to die on the cross--to take away our sins! (The sins that prevent us from entering into eternal life to begin with.)
Study the book of Hebrews for more on this.
"There is therefore now no condemnation to those who are in Christ Jesus" --St. Paul's Letter to the Romans, 8:1
Blessings!
PS I'd rather be sure after the Judgment, not before.
The Judgment took place in AD 70. You quoted Matt. 25; read the whole Olivet Discourse (starting in context in Matthew 23) and you will see that Jesus Himself predicted that the judgment would occur with the destruction of the Temple (which signified the ending of the Old Jewish Covenant.)