These things having been explained, it seems that one point remains: namely, to see what the gate is by which we may enter that most happy house. But the Lord Himself in the Gospel not only showed us the gate, but also foretold that it is exceedingly narrow, and admonished us to strive to enter. For when He was asked, "Lord, are they few that are saved?" (Luke 13), He answered: "Strive to enter by the narrow gate; for many, I say to you, shall seek to enter, and shall not be able. But when the master of the house shall have gone in and shut the door, you shall begin to stand without and knock at the door, saying: Lord, open to us. And He answering shall say to you: I know you not, whence you are; depart from Me, all you workers of iniquity. There shall be weeping and gnashing of teeth." So speaks the Lord, who teaches plainly enough that the gate of the house of God, which is in heaven, is exceedingly narrow, although the house itself is most spacious; and that on account of its narrowness many will not enter who would otherwise gladly enter — and that they will not enter for this very reason, that although they do wish to enter, they will not strive, nor endure any hardship.
Let us explain why the gate of the most spacious house is narrow. A gate has four parts: the threshold, the lintel, and the two sides — that is, four stones, one below, one above, and two at the sides; and in this gate of ours these are four virtues altogether necessary for anyone to be able to enter the heavenly house: faith, hope, charity, and humility. Faith and hope are the side stones; charity is the lintel; humility is the threshold that is trodden underfoot. But all these stones — that is, all these virtues — have so small a length and breadth in themselves that they are exceedingly narrow in themselves and make a most narrow gate. Let us begin with faith. The true Christian faith is beset by straits of such a kind that, unless the human mind does violence to itself and suffers itself, as it were, to be brought into captivity, bound and hemmed in, no one can enter through it. And this is what the Apostle writes in the second Epistle to the Corinthians: Bringing into captivity every understanding unto the obedience of Christ (2 Cor. 10). For the Christian faith proposes many things to be believed which so surpass all reason that it is most difficult to assent to them; and yet it commands them to be believed so certainly and so firmly that a man must be prepared to pour out his life and blood a thousand times rather than deny a single part of the faith. Great are these straits; nor is it a wonder if few surmount them. And this is the reason why so many fall away to the Mohammedans or the heretics: for these have removed the straits of the faith and opened the widest gates — through which, however, one goes not to life but to perdition, according to the word of the Lord in Matthew: Wide is the gate and broad is the way that leadeth to destruction, and many there are who go in thereat (Matt. 7). For every man naturally desires to know, as the Philosopher wrote at the beginning of the Metaphysics; and the mind does not easily assent unless a demonstration, or at least a probable reason, is brought forward. The Apostle Paul experienced this; for although he spoke with infused and acquired wisdom, yet when he preached the resurrection of the dead, there were not lacking those who mocked him, and others who said: What is it that this word sower would say? (Acts 17) And when he proclaimed Christ crucified, he seemed foolish to the Gentiles, and the Jews were scandalized, as he himself testifies in the first Epistle to the Corinthians (1 Cor. 1). Hence also the ancient heretics, in order to widen the narrow gate, devised various errors. For some did away with the mystery of the Trinity, as the Sabellians and Arians; others with the mystery of the Incarnation, as the Nestorians; others with the resurrection of the dead, as the Origenists; and others with still other doctrines. But all these gates — and others, nearly two hundred in number — because they had human architects and lacked a solid foundation, collapsed within a short time; indeed, we would not even know their names had we not read them in the books of Philastrius, Epiphanius, St. Augustine, Theodoret, and the like. But the Mohammedans, who have now spread their sect so far and wide, have removed almost everything that is more difficult in the Christian faith: the Trinity of the divine Persons, the Incarnation of the divine Word, the death and resurrection of the Son of God, the Sacrament of Penance. All the narrow straits were taken away, and the widened gate admits an innumerable multitude.
But the heretics of our time have entered by another road, and have removed especially those straits which pertain not so much to understanding as to action. The Christian faith teaches that all sins are to be avoided — so that an account must be rendered even for an idle word; that if anyone falls into mortal sin, his sins must be confessed to a priest and washed away by sincere contrition and satisfaction; that good works, however laborious and difficult, must be done if they are prescribed by superiors; that the kingdom of heaven is to be merited by good works, as the crown of justice and the reward of labor; that celibacy is to be observed by ecclesiastical and consecrated men, and sacred vows are to be kept. These and similar things, which seemed to make the way narrow, the heretics of this time so removed that they opened a very wide gate. For they preached that faith alone is necessary for salvation, so that a Christian man cannot perish, however covered he may be with all manner of sins, unless he refuses to believe. Likewise, that there is no need to confess sins to a priest — it is enough if one confesses to God; that contrition is not required — it suffices to acknowledge certain errors in the mind; that works of penance and satisfaction are not necessary; that priests are free to exchange celibacy for marriage; that monks and nuns are no less free to despise all their vows; and that prelates cannot oblige their subject peoples to any works of piety. By these and similar doctrines, having removed the straits of the faith, they seemed to themselves to have made a very wide gate of salvation; but in truth they opened the gate that leads to hell, and through it drew with them a huge crowd of frivolous men to perdition.
Nor indeed do all Catholics surmount the straits of faith: for although they believe all that faith teaches, yet because they live otherwise than faith commands, they are proved to be among those of whom the Apostle speaks when he says: They profess that they know God, but in their works they deny Him (Titus 1:16). And for this reason they too escape the straits of faith and enter through the wide gate that leads to perdition. Therefore, if the matter is considered as regards faith, the answer to the question put to the Lord — Are they few who are saved? — will be that few are saved, and that we must therefore strive to enter by the narrow gate.