In the context of the larger teachings of the sermon, this is a segment. Jesus was speaking to those who were in the beginning stages of following Him. Their call is to love, not to judge.
It is so easy to judge those who choose a different path, or who stumble along the way. Jesus was reminding them, reminding us, that we are in no position to judge. We should not waste out energy on judgment.
Then, He promised that all who seek the Kingdom will find it, it is not for us to decide who earned entry.
It’s as simple as knocking on a door to gain entry, but the road is hard. In the greater context of the teachings of the sermon, I think the key is forgiveness. Narrow is the road of the life of the forgiven and narrower still that of the forgiver.
Imagine a world where each person treated every other person as though they stood clean in the sight of God.
Do you want to be treated as though you have been cleansed of all sin and can stand in the presence of God? Treat others with that kind of love.
Practice forgiveness, to its fullest extent, and your house will stand firm.