Today's Gospel coincides in a sad way with the headlines about the earthquake in New Zealand. There, on the other side of the world, a city built not on a hill or on a rock, but on a foundation of sand and silt, suffered loss of life and immense structural damage.
Unless you are an architect or engineer, I suspect you wouldn't tend to think about foundations all that much.
But Jesus seems to have thought a lot about foundations.
He told the parable of the person who paid God lip service, but didn't actually do God's will and said that such a one was building on sand. When it came to making sure his flock would have a home in this world, Jesus built his own house on rock: "You are Peter and on this 'rock' I will build my Church and the gates of hell will not prevail against it."
The opening prayer for today's feast of the "Chair of St. Peter" emphasizes that the "foundation" on Peter's profession of faith is at the service of the unity of the Church. That's why we have a Pope; that's why Peter still has a "chair" from which to teach.