One of the most powerful arguments to refute the Protestant doctrine of Eternal Security (also known as Once Saved, Always Saved) is the example of Judas. The typical objection these Protestants make is that if someone 'falls away' then they were never really saved in the first place, but this claim (aside from being unbiblical) doesn't work with Judas' example. Some will point to John 17:2 which says Judas was "lost," but this refers to his losing his salvation, as will be shown.
The force of my argument rests in the fact that it is impossible to be an Apostle if one is not a true believer in the first place. (This causes problems for Reformed church leadership as well.) If the Protestant
position were correct, the Bible could only have said Eleven were
Apostles, despite the fact it plainly says Jesus chose Twelve (John 6:70). Further, the Bible is very clear that Judas was sent out by Jesus with the other Eleven to perform the same miracles (e.g. cast out demons) and preach the same Gospel (e.g. Mark 6:7-13; Matthew 10:1-4). If that wasn't enough, Acts 1:17 says Judas "was numbered among us and was allotted his share in this ministry," and Acts 1:24-25 records the replacing of Judas by Matthias, when Peter says they need a person to "take the place in this ministry and apostleship from which Judas turned aside." Clearly, Judas was considered a genuine Apostle and thus was (originally) saved.
Nearly every time Judas is mentioned, his infamy traces to one thing: his future betrayal of Jesus, not some non-converted status he had the whole time (e.g. John 6:71).
It is only in John 13 where we see Satan "entered Judas," indicating
Judas consented to the betrayal, but up until then Judas was not possessed
by Satan. Next, look what the Scriptures say that turns the heat up even more on the Protestant position. In John 13:18, Jesus quotes an OT prophecy in regards to Judas, "But the Scripture will be fulfilled, 'He who ate my bread has lifted his heel against me.'"
To share bread with someone in the Hebrew mindset indicates an intimate
relationship; something impossible if Judas was never a believer to
begin with. But that's not all, most of us forget to look up the
prophecy Jesus is quoting (hat tip to Joe for this), which happens to be Psalm 41:9, which says: "Even my close friend in whom I trusted, who ate my bread, has lifted his heel against me."
What a new picture emerges after reading this! Indeed, the idea that
Judas was so close to Jesus up until then shows just how serious and
enormous the betrayal was, since the worst betrayals are those from the
people closest to you. Jesus even calls him 'friend' at the moment of
betrayal (Matthew 26:49-50)! This is unthinkable if Judas was never saved to begin with.