Matthew 7:13-23 in more detail

The following is an abridged version of "The Broad Way Contrasted with the Narrow (Matt 7:13-23)", by Antonio da Rosa, which can be found at the Free Grace Theology blog.

“Enter by the narrow gate… Because narrow is the gate and difficult [lit: constrained] is the way which leads to life, and there are few who find it.”

Jesus is exhorting his audience to be careful to start things out in the right way; to get started at the right place. His audience must be careful that they go through the gate that leads to life and not to destruction. In terms of the larger audience, and the disciples He is saying: Be sure that your starting point is the correct starting point.
The narrow gate is Christ:
John 10:9 - I am the door. If anyone enters by Me, he will be saved.
John 14:6 - Jesus said to him, "I am the way, the truth, and the life. No one comes to the Father except through Me.
The way to life is constrained, narrow. There is but one gate, Jesus Christ, and there is only one way to enter it, by faith alone in Christ alone.
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...for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it.

The wide gate with the broad path represents every other “way” to salvation that is not through Christ, through faith in His Name. This would inlude every false religion in the world from animism to humanism; Islam to Buddhism; Hinduism to Judaism, and all others in between.
But let us not stop here. The “way that leads to destruction” is also paved with “Christian” doctrines and false “gospels”. It is tiled with sincerity, good intentions; it is cemented with counterfeit prophets and bible teachers. This road attracts a lot of attention with high profile sects, denominations, and doctrinal positions; with radio bible teachers and seminary presidents; with global organizations and social activists. Those that beckon the world to this path proclaim far and wide the doctrines of Rome; the mysticism of Mormonism; the angelology of the JWs; the self-salvation of Arminianism; the costly conversion of Lordship Salvation; and the exclusivism of Traditionalism.
Any teaching that requires anything in addition to simple faith alone in Jesus Christ alone, the Guarantor of eternal life and resurrection to the believer in Him for it, diverts its adherents from the narrow gate and detours them to the broad way that leads to destruction.
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One of the problems that people have in finding the correct gate is that there are people who tell them the wrong gate! There are people who profess prophetic ability or profess to be sent by God and they lead them astray. Jesus immediately follows the exhortation to enter into the correct gate by a warning against the false prophets. The way that the false prophets are known is by their fruits.

Beware of false prophets, who come to you in sheep's clothing, but inwardly they are ravenous wolves. You will know them by their fruits.

The very first thing that we should notice concerning the prophets who lead people astray with their false messages, doctrines, and teachings, is that they come to the people “in sheep’s clothing.”The Traditional interpretation of this passage is that men must gain assurance of their salvation by their works. This passage is so obviously not talking about this!
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The false prophets come to the people “in sheep’s clothing”. What is the implication here? -- There is no way to tell the false prophet by their outer appearances! They look, smell, act, and behave like sheep. They are wolves in sheep’s clothing! Every outward appearance is that of a Christian. So “fruit” cannot mean their conduct! Fruit is the doctrine that they preach; the fruit is the message that they bring. If they preach anything but eternal salvation by grace through simple faith in Jesus Christ, they are false prophets. If they bring a message that is contrary to what Jesus taught then they are false prophets.
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Many will say to Me in that day, "Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?"

Jesus in His mercy tells us what many will say to Him in that Day: First, they will acknowledge the Lordship of Jesus Christ, addressing Him as 'Lord.' Not only will they say it once, they will repeat it: 'Lord, Lord.' Recognizing the gravity of the situation, they will plead for their lives. This repetition of 'Lord' may also suggest that they think they are on familiar terms with Jesus.
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Those who have heeded the message of the false prophets will plead their case with Jesus. They will be all too sincere. They will not be conscious charlatans trying to pull the wool over Jesus’s eyes. They will be all too serious as they point to both to their allegiance to Christ and to their works in His name!
These aren’t Buddhists, Hindus, etc. They are “Christians” who are offering their works “in Your [Jesus’] name” (three times!). These are the ones who obeyed the words of the false prophets who led them down the road to perdition. They did not do the will of the Father which was to trust solely in Jesus Christ for their entrance into the kingdom. They will be condemned for their words which betray their trust in their works!

And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!

Rom 3:20-28 - Therefore by the deeds of the law no flesh will be justified in His sight, for by the law is the knowledge of sin.
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Where is boasting then? It is excluded. By what law? Of works? No, but by the law of faith. Therefore we conclude that a man is justified by faith apart from the deeds of the law.
"Jesus will describe these people as ‘you who practice lawlessness.’ Now if we had seen these people on earth—and perhaps we have seen some of them—we may not have reached that conclusion. After all, we would have seen these church leaders prophesying, casting out demons, and performing supernatural wonders, all in the name of Jesus. The Roman Catholic Church-State would have declared them saints. The ersatz Evangelicals would have made them best-selling authors and celebrities. But Jesus calls them ‘you who practice lawlessness.’ Why?
He has already told us why. All of these extraordinary and wonderful works done in the name of Jesus are lawlessness, because they are done for the purpose of obtaining salvation. These works are lawlessness because they involve an illegal use of the law. The law, Paul tells us, is given for the knowledge of sin. It is not given that we sinners might use it to gain entrance into heaven. Conviction of sin, not salvation, is the purpose of the law. Legalism, because it is an illegal use of the law, is lawlessness. ‘But we know that the law is good if one uses it lawfully,’ Paul told Timothy. But using the law in an effort to obtain heaven is not lawful; it is an illegal use of the law; it is lawlessness." (John W. Robbins, Ibid.)
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Lets get some perspective. In the newest edition of “Operation World” (A prayer guide for missions) we find that the world’s population is around 6 billion. Out of those 6 billion, roughly 2.5 billion are considered “Christian”.
350 million Protestants
303 million Indepentants
67 million Anglicans
420 million Evangelicals
345 million Charismatics
1 billion Catholics
212 million Orthodox
Christians account for roughly 1/3rd of the world’s population. This does not qualify for a “few”.
Christ contrasts the terms “many” and “few”. Only a “few” find the correct gate and enter thereby.
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If my [Antonio's] crude analysis of “few” meaning 8-15% of the population is correct, than we have a problem. 33% of the world’s population is “Christian”; much too high of a figure to denote a relative “few”. What can we glean of this? That much of “Christianity” is not saved, but needs to be evanglized. Why? The gospel has been corrupted by thousands of false teachers who preach a distorted gospel.
The Wide Gate and Broad Road: "there are many who go in by it"
The Narrow Gate and Constrained Way: "there are few who find it"