15 Therefore did the Lord graft in at once the wild olive tree, when He said, “Many shall come from the east and west, and shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of heaven;” that is, they shall be grafted into the good olive tree. For Abraham, and Isaac, and Jacob, are the roots of this olive tree; “but the children of the kingdom,” that is, the unbelieving Jews, “shall go away into outer darkness.” The “natural branches shall be broken off,” that the “wild olive tree may be grafted in.”
Now why did the natural branches deserve to be cut off, except for pride? Why the wild olive tree to be grafted in, except for humility? Whence also that woman said, “Truth, Lord, yet the dogs eat of the crumbs which fall from their masters' table.” And thereupon she hears, “O woman, great is your faith.” And so again that centurion, “I am not worthy that You should come under my roof.” “Verily I say unto you, I have not found so great faith, no, not in Israel.” Let us then learn, or let us hold fast, humility. If we have it not yet, let us learn it; if we have it, let us not lose it. If we have it not yet, let us have it, that we may be grafted in; if we have it already, let us hold it fast, that we may not be cut off.
Source: Sermons on Selected Lessons of the New Testament (New Advent)