So never doesn't mean never? Jesus did not say I once knew you, but don't anymore. He clearly stated I never knew you. The term "know" implies intimate, experiential knowledge, through a relationship with Him, not merely theoretical knowledge. (John 17:3) If they truly believed in Jesus unto salvation, then they would have said, 'Lord, Lord' didn't YOU (Romans 3:24-28) instead of didn't 'WE.' They were obviously trusting in works for salvation and not in Christ alone. Jesus described these pseudo Christians as "you who practice lawlessness" which is not descriptive of genuine believers. (1 John 3:7-10)
Let me point out a couple of things here, because the contention is not in the word 'never'.
In the Bible, 'knowing' is used in the context of intimacy in a relationship, and, the lack of that relationship altogether. And notice, in this passage, it is not about them knowing him,
but him not knowing them. Does he mean he never knew these people intimately, or he did not know them at all? Biblically, it could mean either.
Their lawlessness is not the exercise of their spiritual gifts,
it's their lack of obedience to the sayings of Christ.
We don't know if these spiritual gifts were fake or for real. The parallel passage (Luke 13:24-30) suggests he is talking about the common everyday people who walked the streets with him who do not have spiritual gifts, not the leaders of the Jews who would indeed have legitimate spiritual gifts despite them having neither an intimate relationship, or a relationship at all with Christ. But, on the other hand, the context of the Matthew 7 passage is false prophets. So that suggests he is talking about the leadership of Israel who could have legit spiritual gifts.
He does seem to be addressing a
particular group of people for whom 'never' applies, not broad stroking all people who live lawlessly in the exercise of their spiritual gifts. We are the one's who are saying Jesus is writing hard and fast truth about ALL people, everywhere, in all times who fit this description. Jesus doesn't say that in the passage. We interpret it that way.
So you see, this passage isn't as cut and dry as people make it out to be. Never means never in the passage. It's all these other things that I listed that are in contention.