I wouldn't say only. There are commentaries too.
Matthew Henry's Concise Commentary
7:12-14 Christ came to teach us, not only what we are to know and believe, but what we are to do; not only toward God, but toward men; not only toward those of our party and persuasion, but toward men in general, all with whom we have to do. We must do that to our neighbour which we ourselves acknowledge to be fit and reasonable. We must, in our dealings with men, suppose ourselves in the same case and circumstances with those we have to do with, and act accordingly. There are but two ways right and wrong, good and evil;
the way to heaven and the way to hell; in the one or other of these all are walking: there is no middle place hereafter, no middle way now. All the children of men are saints or sinners, godly or ungodly. See concerning the way of sin and sinners, that the gate is wide, and stands open. You may go in at this gate with all your lusts about you; it gives no check to appetites or passions. It is a broad way; there are many paths in it; there is choice of sinful ways. There is a large company in this way. But what profit is there in being willing
to go to hell with others, because they will not go to heaven with us? The way to eternal life is narrow.
The way to heaven is hard – Matthew 7:13-14 -
http://www.easyenglish.info/bible-commentary/matthew4-13-im-lbw.htm
v13 ‘Enter in through the narrow gate. There is a wide gate and a broad road.
But that way leads to hell. Many people go through that wide gate. v14 But the gate is small that leads to life. And the road is narrow. Few people find that way.’
Verses 13-14 There are two ways in life. People must decide which way they will go. It is important to make the right choice. Jesus describes this as the choice between two gates and two roads. There are two ways and two final places. Jesus tells his *disciples to take the way through the narrow gate. This gate and the narrow road is the way to *eternal life. The end of this road is a home in God’s *kingdom. It is harder to find the narrow gate than to find the broad gate. The narrow road is harder to follow than the broad road. There are more people on the broad road than on the narrow road. The broad road is easy to follow but it leads to death and permanent loss.
To enter through the narrow gate means to come to Jesus in *faith. Then we follow him. He said that he is the way, the truth and the life (John 14:6). There is no other way to *eternal life.
