One summer many years ago I acted as chaplain for a week in a home for old people. It was about this time of the year and we were reading these sections of the Book of Genesis. Some of the older people were scandalised at what Abraham was getting up to in his old age and complained to me that 'we should not have to listen to this kind of carry on during Mass'.
It is indeed a bit shocking. Today's reading, for example, speaks about a kind of surrogate motherhood involving Sarai, Abram and Hagar. Sarai is keen to give her husband a child and does so using the womb of her servant Hagar. As soon as the maid is pregnant, however, she begins to feel superior to her mistress who is, for the moment, childless. Sarai's mood changes and she is not as keen on the situation as she was before it happened. Sarai wants to get rid of Ishmael and his mother, and Abram goes along with this. Ishmael is a wild ass of a man, not the son of the promise as Isaac was to be, but still not falling outside the reach of God's providence. Sarai and Abram might want to see the back of Hagar and Ishmael but God has a place for them in his plan - a plan he is working out through Abram - and it gives Ishmael some entitlement in the household of his father. What exactly the story of Hagar and Ishmael is trying to explain remains obscure, though they will figure later in Christian reflections on grace, freedom, and God's choice.
One of the issues raised here is that of legitimacy: how does a son become entitled to the inheritance of his father? Ishmael has a problem because he is the son of a servant. He is, it is true, the son of Abraham but not a fully legitimate one. He has, it seems, some rights in the household but not the full rights of a son born to a free woman. This is Paul's use of the story later, in Galatians, where Hagar represents the earthly Jerusalem, an unfree city, and Sarah represents the heavenly Jerusalem, the place of freedom God has established for all the children of Abraham.
The gospel reading blows apart all these older, more primitive, understandings of legitimacy and entitlement. The key to the door of the Father's kingdom is not now anything to do with the circumstances of one's natural birth. It is connected simply and exclusively with whether or not one acts on the will of the Father. It is not enough to hear it and to know it. The man building his house on rock is the one who not only hears the words spoken by Jesus but also acts on them. This is the new family of Abraham. He is our father in faith, and it is a faith in practice, a faith formed by the new commandment of love that characterises and unites the members of this family of Abraham.
In a text that anticipates Paul's hymn to love in 1 Corinthians 13, Jesus says that it is not enough to say 'Lord, Lord'. It is not enough to prophesy or to drive out demons. It is not enough to work mighty deeds. It is not enough to claim Abraham or Moses or David as our father. What is required is that a person hear the words of Jesus and act on them. It is at once simpler, and much more difficult, than any other way of belonging. We simply have to act on the teachings of Jesus which we have been listening to in the Sermon on the Mount. But if we are to act on those teachings in the way Jesus has asked, then we need the love of God to be poured into our hearts. It is the Holy Spirit, the bearer of that gift, who makes us to be the children of God, heirs with the Son, practitioners of the Law, people entitled to be in the household of the Father with an entitlement that is, purely and simply, His gift, renewed each day.