From: Luke 13:22-30
The Narrow Gate
 He (Jesus) went on his way through towns and villages, teaching, and journeying toward Jerusalem.  And some one said to him, "Lord, will those who are saved be few?" And he said to them,  "Strive to enter by the narrow door; for many, I tell you, will seek to enter and will not be able.  When once the householder has risen up and shut the door, you will begin to stand outside and knock at the door, saying, 'Lord, open to us.' He will answer you, 'I do not know where you are from.'  Then you will begin to say, 'We ate and drank in your presence, and you taught in our streets.'  But he will say, 'I tell you, I do not know where you come from; depart from me, all you workers of iniquity!"  There you will weep and gnash your teeth, when you see Abraham and Isaac and Jacob and all the prophets in the kingdom of God and you yourselves thrust out.  And men will come from east and west, and from north and south, and sit at table in the kingdom of God.  And behold, some are last who will be first, and some are first who will be last."
23-24. Everyone is called to form part of the Kingdom of God, for he "desires all men to be saved" (1 Tim 2:4). "Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience: those too may achieve eternal salvation. Nor shall divine providence deny the assistance necessary for salvation to those who, without any fault of theirs, have not yet arrived at an explicit knowledge of God, and who, not without grace, strive to lead a good life. Whatever good or truth is found among them is considered by the Church to be a preparation for the Gospel and given by him who enlightens all men that they may at length have life" (Vatican II, "Lumen Gentium", 16).
Certainly, only those who make a serious effort can reach the goal of salvation (cf. Lk 16:16; Mt 11:12). Our Lord tells us so by using the simile of the narrow gate. "A Christian's struggle must be unceasing, for interior life consists in beginning and beginning again. This prevents us from proudly thinking that we are perfect already. It is inevitable that we should meet difficulties on our way. If we did not come up against obstacles, we would not be creatures of flesh and blood. We will always have passions that pull us downwards; we will always have to defend ourselves against more or less self-defeating urges" ([St] J. Escriva, "Christ Is Passing By", 75).
25-28. As at other times, Jesus describes eternal life by using the example of a banquet (cf., e.g., Lk 12:35ff; 14:15). Knowing the Lord and listening to his preaching is not enough for getting to heaven; what God judges is how we respond to the grace he gives us: "Not everyone who says to me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of my Father who is in heaven" (Mt 7:21).
29-30. Generally speaking, the Jewish people regarded themselves as the sole beneficiaries of the messianic promises made by the prophets; but Jesus proclaims that salvation is open to everyone. The only condition he lays down is that men freely respond to God's merciful call. When Christ died on the cross the veil of the temple was torn in two (Lk 23:45 and par.), a sign of the end of the distinction between Jews and Gentiles. St Paul teaches: "For he [Christ] is our peace, who has made us both one, and has broken down the dividing wall [...] that he might create in himself one new man in place of the two, so making peace, and might reconcile us both to God in one body through the cross, thereby bringing the hostility to an end" (Eph 2:14-16). Therefore, "all men are called to belong to the new people of God. This people therefore, whilst remaining one and only one, is to be spread throughout the whole world and to all ages in order that the design of God's will may be fulfilled: he made human nature one in the beginning and has decreed that all his children who were scattered should be finally gathered together as one" (Vatican II, "Lumen Gentium", 13).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.