Luke 13:22 - 23 And he went on his way through towns and villages, teaching and journeying toward Jerusalem and someone said to him Lord [master], will those who are saved be few?

Jesus answer to this question is on the basis that the average religious Jew-believed they were in the kingdom of God. The person asking the question would be thinking only the morally bad are out, and the morally good are going to be saved and in.

The average religious Jew would be thinking that being a natural descendent of Abraham having the law, the land, the temple, the worship etc. meant they were in the kingdom.

But without receiving their Messiah, the rest was just dead religion. This is why Jesus uses the metaphor strive to enter through the narrow door.

In John's Gospel the narrow door is Jesus himself. In the metaphor Jesus is telling us that the only way in to the kingdom is through him. The door is too narrow to squeeze through any moral deeds to earn salvation.

Repentance and faith in Christ is not only repenting of evil deeds done before God, it is repenting of good deeds done for selfish and wrong motives. This is why Jesus says many will seek to enter but will not be able to, because they will not die with him, and accept that the whole old Adam deserves death, and rise with him to a new creation.

Not the labors of my hands can fulfill thy laws demands... Thou must save, and that thou alone... Nothing in my hand I bring simply to the cross I cling naked come to thee for dress, helpless, look to thee for grace...