Matthew 7:21-23 is talking about people who believe in a works based salvation...

Matthew 7:21-23
21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.

MY ANSWER RIGHTLY DIVIDED:

This is how you break a verse down, rightly divide, and let scripture define itself...

So these people cast out devil's IN HIS NAME, prophesized IN HIS NAME, and did many wonderful works IN HIS NAME...

No doubt they claim the name of Jesus...

But he says depart from me "I NEVER KNEW YOU" not to be confused with "I used to know you"...

You see some think they lost their salvation, but it is clear they didn't do the "WILL" of the Father....

In this instance we have to let scripture define scripture...

So what is the will of the Father???

John 6:39-40
39 And this is the Father's will which hath sent me, that of all which he hath given me I should lose nothing, but should raise it up again at the last day.
40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.

So we can see here that according to verse 39 he never knew them, they did not lose salvation, as the will of the father is that all that are given to Jesus he will lose NOTHING...

Also verse 40 says the will of the father in regards to salvation is that whoever believes WILL have everlasting life....

So even though these people did all these WONDERFUL WORKS in his name, they did not believe never being forgiven of their iniquities... They trusted in their works, and actually boasted before God in those works, and we can clearly see in Ephesians 2:8-9 is not of works...

Ephesians 2:8-9
8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
9 Not of works, lest any man should boast.

This is referring to the "man of lawlessness." It is a group of people that would develop from the great apostacy that Paul foretold would happen after the death of the apostles. It had already started while they were still alive but while they were alive they were able to keep it at bay. After the death of the last apostle, John, toward the end of the first century then Satan was able to sow the weeds in the Christian congregation. Over time, by the 3rd century C. E., an apostate form of Christianity was embraced by the Roman pagan Emperor Constantine and declared the State religion. The apostate Catholic Church, together with its "clergy" and "laity" distinction began to rule.

Paul says concerning this clergy of Christendom (which later embraced those of the Protestant reformation as well):

"3 Let no one lead you astray in any way, because it will not come unless the apostasy comes first and the man of lawlessness gets revealed, the son of destruction. 4 He stands in opposition and exalts himself above every so-called god or object of worship, so that he sits down in the temple of God, publicly showing himself to be a god. 5 Do you not remember that when I was still with you, I used to tell you these things?

6 And now you know what is acting as a restraint, so that he will be revealed in his own due time. 7 True, the mystery of this lawlessness is already at work, but only until the one who is right now acting as a restraint is out of the way. 8 Then, indeed, the lawless one will be revealed, whom the Lord Jesus will do away with by the spirit of his mouth and bring to nothing by the manifestation of his presence. 9 But the lawless one’s presence is by the operation of Satan with every powerful work and lying signs and wonders 10 and every unrighteous deception for those who are perishing, as a retribution because they did not accept the love of the truth in order that they might be saved. "- 2 Thessalonians 2:3-10.

This "man of lawlessness" or "worker of lawlessness" has been exposed by Jesus Christ as being the clergy of Christendom. They profess Jesus' name, and claim to perform many powerful works in his name, but they are workers of lawlessness.

The will of the Father cannot be expressed in words. If you using mind to express that will, Jesus will respond - "I never knew you". One has to exist where Jesus exists. Not in mind but in your soul. The very root of our being (aka the vine).