Many will say to me on that day, “Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?” Then I will tell them plainly, “I never knew you. Away from me, you evildoers!”
(Matthew 7:21-22)

“Lord, lord” is a phrasing that doesn’t correlate well with an English equivalent. The use of repetition gives emphasis to the word “lord” (Greek Kyrie, “lord/master”).

…the reduplication of the title “Lord” denoting zeal in according it to Christ.
(Jamieson Fausset Brown Bible Commentary)

Elsewhere in the Bible, this kind of repetition in addressing someone demonstrates a high degree of familiarity, even of intimacy. Jesus is no mere acquaintance here. He isn’t just the guy down the street. Those approaching him on that great and terrible Day of Judgement see themselves as insiders. They claim to have done great and mighty things for Jesus. They are prophets of the Lord!

Yet Jesus sees through them, their deeds are found lacking, and they are rejected. And they are rejected quite harshly. Jesus answers these “insiders” by saying, in essence, “Really? You say we’re best buds? Um, no, I don’t believe we’ve met. Get lost.” The late theologian R. C. Sproul called this passage “the most terrifying passage in the New Testament”: “In the final analysis it isn’t do you know Jesus? The question is, does Jesus know you?” (podcast “Build on the Rock”, available at iTunes).

Many questions are raised here. Are these false disciples actually “ex”-disciples, or apostates? Can lapsed believers lose their salvation? Some controversy within Christianity exists as to whether a person can truly experience “saving faith” and then fall away later. I won’t attempt to settle that debate here. Furthermore, that doesn’t seem to be the real issue in this passage.

The immediate context of this passage is the “Sermon on the Mount”, in which Jesus has much to say about hypocrites, those who do good works for show and self-aggrandizement. They are actors with two faces. They pray loudly. They give large sums to the Lord’s work, making sure that their coins rattle and clink loudly as they are poured into the collection. They make themselves look miserable during fasts, so that others don’t miss the fact that they are fasting. They are narcissists within the community of faithful. This taints their good deeds. They may lay claim to being prophets, but false prophets they are–“wolves in sheep’s clothing.”

It would be tempting then to say that works are unnecessary: “Empty works are bad, so merely believe in God in your heart, and all will be well.” But Jesus doesn’t let people off that way. He is not contrasting deeds with non-deeds. The passage which immediately follows the frightening disowning of many seemingly zealous followers, also clearly stresses good works. Two kinds of doers of good works are contrasted, not merely those who do works vs those who don’t.

The question is, on what kind of foundation are those works built? Are they built on love for God? Are they built upon love of self?

Jesus praises those who hear, and then do the will of their lord. For them the word of the master sinks in, and is taken to heart. It produces a response of love that results in good works. Neither the empty works of the faithless, done for show, nor empty words of a profession of faith, devoid of works, are sufficient evidence of a heart that has been really touched by God.

Jesus here connects the hearing with doing, much as James did later in his discourse on the relationship between saving faith and works:

What good is it, my brothers, if someone says he has faith but does not have works? Can that faith save him? If a brother or sister is poorly clothed and lacking in daily food,and one of you says to them, “Go in peace, be warmed and filled,” without giving them the things needed for the body, what good is that? So also faith by itself, if it does not have works, is dead.
But someone will say, “You have faith and I have works.” Show me your faith apart from your works, and I will show you my faith by my works. You believe that God is one; you do well. Even the demons believe—and shudder! Do you want to be shown, you foolish person, that faith apart from works is useless? Was not Abraham our father justified by works when he offered up his son Isaac on the altar? You see that faith was active along with his works, and faith was completed by his works; and the Scripture was fulfilled that says, “Abraham believed God, and it was counted to him as righteousness”—and he was called a friend of God. You see that a person is justified by works and not by faith alone. And in the same way was not also Rahab the prostitute justified by works when she received the messengers and sent them out by another way? For as the body apart from the spirit is dead, so also faith apart from works is dead.
(James 2:14-26)

Where the heart is–where our faith is–there good deeds will follow. “By their fruit ye shall know them” says Jesus elsewhere. As the great preacher Charles Spurgeon once stated:

ONE of the best tests by which we may try many things is to ask, “How will they appear at the day of judgment?” Our Lord here says, “Many will say to Me in that day.” He used no other word to describe that memorable period because that terse, brief expression suggests so much—“in that day”—that terrible day—that last great day—that day for which all other days were made—that day by which all other days must be measured and judged. I pray, dear friends, that we may, each one of us, begin to set in the light of “that day” the things that we most prize. The riches upon which you have set your heart, how will their value be reckoned “in that day,” and how much of comfort will they afford you then? As for the way in which you have been spending your wealth, will that be such as you will remember “in that day” with satisfaction and comfort? Value your broad acres and your noble mansions, or your more moderate possessions, according to this gauge of their real worth—how will they be valued “in that day”? And as to the pursuits which you so eagerly follow, and which now appear so important to you that they engross the whole of your thoughts, and arouse all your faculties and energies, are they worthy of all this effort? Will they seem to be so “in that day”?