The Scriptural evidence is plentiful that Judas Iscariot was once saved, but it is often overlooked or avoided. For example, we read:
When he was alone, the Twelve and the others around him asked him about the parables. He told them, “The secret of the kingdom of God has been given to you. But to those on the outside everything is said in parables so that, ‘they may be ever seeing but never perceiving, and ever hearing but never understanding; otherwise they might turn and be forgiven!’” (Mark 4:10-12)
Because Judas Iscariot was one of the Twelve (Mt 10:1-4) and the Twelve (as well as all Christians) are of the other group distinguished from those on the outside, this proves he too was given the ability to understand the secrets of the kingdom that God revealed through the parables. Beyond that, Judas had been forgiven at that point, unlike those on the outside!
The significance of Judas Iscariot once possessing salvation is one of the deathblows to the false gospel of once saved always saved. Why? Because he ended up in hell after his death (Mk 14:21; Jn 17:12). Hence, he somehow lost his salvation, even though he had become one of the Lord’s original apostles!
[For much more proof that Judas Iscariot was once saved, please consult, The Believer’s Conditional Security by Dan Corner, pages 279-286.]