Hi again,

That is why, we first have to establish who these people really are. Sure, there are those who can perform counterfeit miracles. I do not deny this. BUT they perform counterfeit miracles NOT in the name of Jesus'.

That is the crux & is the main contrast.

But in this situation, that is not the case. These people actually claimed, that they performed all these in the name of Jesus'. 

That is also why, i quoted Matthew 12:22-28 for your benefit. ( You can also refer to Luke 11:15 - 20 )  Here it is again :
Matthew 12:22-28

A House Divided Cannot Stand

22 Then one was brought to Him who was demon-possessed, blind and mute; and He healed him, so that the [a]blind and mute man both spoke and saw.

23 And all the multitudes were amazed and said, “Could this be the Son of David?”

24 Now when the Pharisees heard it they said, “This fellow does not cast out demons except by Beelzebub, the ruler of the demons.”

25 But Jesus knew their thoughts, and said to them: “Every kingdom divided against itself is brought to desolation, and every city or house divided against itself will not stand.

26 If Satan casts out Satan, he is divided against himself. How then will his kingdom stand?

27 And if I cast out demons by Beelzebub, by whom do your sons cast them out? Therefore they shall be your judges.

28 But if I cast out demons by the Spirit of God, surely the kingdom of God has come upon you.
These people claimed that they cast out demons. They also claimed that they did it in the name of Jesus. Therefore, we objectively look at the act itself.

How is it possible to successfully cast out a demon from someone, unless you really have the power & authority of God to do it?  Which they actually did perform.

NOW UNLESS you say that they're all liars & just pretended to perform exorcism, then you've already made up your mind & i rest my case.

But just so you know, both you & i weren't there. So if they say what they did is true, which the Bible says so as well, then we'll just have to assume that they did INDEED perform such miracles & exorcism THROUGH THE NAME OF JESUS.

They already declared that they performed the 'casting out of demons' through Jesus' name. Which means they credited God for it. They did not cast demons out by Buddha, not Mo, not Vishnu, etc.

You must understand this, a non-Christian will not say things that give glory to God.
Case in point :

Luke 9:49-50

49 And John answered and said, Master, we saw one casting out devils in thy name; and we forbade him, because he followeth not with us.

50 And Jesus said unto him, Forbid him not: for he that is not against us is for us.
Okay, so we can conclude that these folks were indeed performing miracles & casting out demons in the name of Christ.

Next,

The reason why i said the premise used by the previous poster is flimsy, is because of the English word play on 'never'. You have to be careful with how the whole sentence is said in its original text.

For that, i can't help you, because i don't know Hebrew or Greek or Aramaic. So you'll have to take the english translations at face value. Like i quoted from the Contemporary Eng ver, it says :
But I will tell them, "I will have nothing to do with you! Get out of my sight, you evil people!" - Matthew 7:23 (Cont Eng ver)

Notice it doesn't say, ' I never knew you'.

You cannot just say, ahh, ' I never knew you'. So that's it then. That means these people were all liars from the beginning. That is not good exegesis IMHO.

I'm not calling these people liars for claiming what they could perform. I believe they were once genuine believers. Neither am i saying that God is a liar. In this context, God is denying them entrance into the Kingdom.
Again, if you missed out on the verse that i left you, here it is :
"But when a righteous man turns from his righteousness and practices iniquity, committing the same abominations as the wicked, will he live? None of the righteous acts he did will be remembered. Because of the unfaithfulness and sin he has committed, he will die." - Ezekiel 18:24 

For me, it's very simple. There are 2 camps here :
Camp 1 :  Those who believe in 'Once Saved, Always Saved'. So by default, they will naturally reinforce their view points, by saying that these people weren't saved to begin with. Jesus never knew them from the start.
Camp 2:    Those who believe that while their Faith were genuine at some point in their lives, it fizzled out towards the end & did not keep the Faith. These will hear those terrible words which you quoted in verse 23.
It's obvious to you by now, as to which camp i belong to 
Finally, coming back to the English translations. Just to reinforce my point :

You must have seen the word 'Saved', in the Bible countless times. You also hear people say often, "I was saved 10 years ago."

However, the word 'Saved' in the Bible is seldom in the past tense. The more accurate translation is, 'we are in the process of being saved'. It's not completely done yet. Interesting ain't it?

For this, you'll have to do your own D.D.   

I'll just leave you with one of many explanations : https://www.simplybible.com/f066-sure-saved...hree-tenses.htm
Hope it helps