"Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat: Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it." Matthew 7:13-14
Unbelievers and naysayers call Christians narrow-minded. The truth is that non-believers and naysayers are the narrow-minded. How can I say that? Easily. Before you have Christ your entire outer world is within the bounds of what scientist have discovered and your inner world is the expanse of the natural man's mind, concentric at best. Talk about narrow. Once you have Christ you understand that all the worlds that you can see, even with the most powerful telescopes, is just a handful of your outer world. Your outer world goes beyond and includes heaven. Your inner mind is expanded and you have the mind of Christ as it is developed by the Holy Spirit of God within. You can see further and deeper into a situation and your inner world is vast and capacious.
Note: OK, that has not been your experience and many of the Christians that you know are narrow minded, but that is not the way of Christ; that is way of the religious, not to be confused with, the righteous in Christ. It is totally true that religion has steered a great many into a narrow and sometimes suffocating array of rules and regulations that are not freeing at all. But don't blame God for the misuse of His plan by narrow minded religious zealots. They do not represent Christianity, they represent their religious tenets of faith. Remember what Jesus said to some of the religious narrow at the time: "generation of vipers", Ye serpents", "you are like whited sepulchers (caskets)", "which indeed appear beautiful outward, but are within full of dead men's bones." Narrow minded is not Christlike.
Strait is the gate is referring to the direction inside the gate. If you were in a tunnel, the tunnel is strait, not curving around and no exits to the left or the right. The way of passage to God is strait through the gate that leads to God straight ahead.
Narrow is the way has nothing to do with narrow-minded. It has everything to do with the means by which one must come to God. God designed you to come to to Him through Christ. There is no other way. There is no spiritual ladder based upon levels of intuition or restraint of specific activities. The atoning blood of Jesus is the only way to God. That's what narrow is referring to in this passage.
Maybe that's why there are few that find it. It's so simple and so easy to enter into the strait gate and follow the narrow passage to holy God. God designed it this way so that everyone could easily come in and partake. But man is hardened by such an invitation from God. Man wants it to be difficult and easy to distinguish who is doing it best and who is trying harder and who is doing the most. Man's corrupted and nurtured ego is the wide gate and his foolishness the broad path and through it man finds himself in the end, with much disappointment.
You can start out on the broad path and still find your way, but few there are that find it. Once you have wandered aimlessly in the vast wasteland of the broad path, it's hard to tame the ego, it's hard to see clearly and it's hard to give it up, even if it is killing you. Because on the broad path there are offers of a great many illusions, some of them can make you think you have found your god, and you did.