Strive to enter through the narrow gate, for many, I tell you, will attempt to enter but will not be strong enough.
After the master of the house has arisen and locked the door, then will you stand outside knocking and saying, 'Lord, open the door for us.' He will say to you in reply, 'I do not know where you are from.' And you will say, 'We ate and drank in your company and you taught in our streets.' Then he will say to you, 'I do not know where (you) are from. Depart from me, all you evildoers!'
And there will be wailing and grinding of teeth when you see Abraham, Isaac, and Jacob and all the prophets in the kingdom of God and you yourselves cast out.
He makes this important point:
On an obvious, historical level, Jesus seems to be speaking about certain Jews of his day. Assuming he himself is the "master of the house," he has himself saying someday to certain people in the parable "I don't know where you come from," banishing them permanently from the household of God they want to enter. Not a few Jews of Jesus' day rejected him despite having eaten and drunk in his company and heard him teach in the streets. And Jesus duly warns them. But it's never that simple. The Lord's words apply as much to the future, to his Church, the new Israel, as to those present when he walked the earth. It is quite conceivable that some who are baptized, who are raised in the true Faith, who go to church and take communion often, will find themselves being told at the end "I don't know where you're from. Depart, evildoers!" Some people who are formally in the Church, the household of God, are not followers of Christ in their hearts, despite claiming to be and having a velleity, as distinct from a will, to do so. And they show that by how they live.
