If they had been of God they’d have continued with us doesn’t mean they were never with us. It simply means they were not of God at their departure, which is why they didn’t continue with us. Happens all the time.
Concerning Judas, he by transgression fell from the ministry and apostleship (
Acts 1:25), and you cannot fall from a place you were never in. He also had the same power as the apostles had (
Matthew 10:1,
8;
Mark 3:14-15,
6:7;
Luke 9:1), and to claim that Judas was never truly saved is to imply that Christ empowered a child of the devil to cast out demons by His own authority, just as He did the other apostles.
Yet Christ Himself refuted the Pharisees when they accused Him of casting out demons by the power of Beelzebub.
“Any kingdom divided against itself is laid waste; and any city or house divided against itself will not stand. If Satan casts out Satan, he is divided against himself; how then will his kingdom stand?” (
Matthew 12:25-26).
No one could answer, because Christ had exposed a clear and undeniable truth. If He had truly authorized a child of the devil to cast out demons, that would have contradicted the very argument He used against the Pharisees.