God chooses Abraham
59 In order to gather together scattered humanity God calls Abram from his country, his kindred and his father's house,16 and makes him Abraham, that is, "the father of a multitude of nations". "In you all the nations of the earth shall be blessed."17
Abram was most likely a polytheist, a believer of many gods in the land of Canaan. He was an old man with a wife who was barren. Yet God must have seen goodness in this man who might have thought that his life was settled.
60 The people descended from Abraham would be the trustee of the promise made to the patriarchs, the chosen people, called to prepare for that day when God would gather all his children into the unity of the Church.18 They would be the root on to which the Gentiles would be grafted, once they came to believe.19
Since people believe in many gods and/or have erroneous conceptions of the true God. Our Lord chose a determinate man and his descendants in order to reveal Himself to them and through them to all people and show that there is only one God.
61 The patriarchs, prophets and certain other Old Testament figures have been and always will be honoured as saints in all the Church's liturgical traditions.
We know by faith that the patriarchs, prophets and certain others referred as just of the O.T. are in Heaven now (not before being liberated from Abraham's Bosom or Limbo of the Fathers by Christ when He descended into this place) for the Church acknowledges them as Saints.
God forms his people Israel
62 After the patriarchs, God formed Israel as his people by freeing them from slavery in Egypt. He established with them the covenant of Mount Sinai and, through Moses, gave them his law so that they would recognize him and serve him as the one living and true God, the provident Father and just judge, and so that they would look for the promised Saviour.20
God showed the sons of Israel that He is the Almighty God with His miraculous deeds and His loving care. Our Lord also instructed them the correct way of worship and fellowship with Him.
63 Israel is the priestly people of God, "called by the name of the LORD", and "the first to hear the word of God",21 The people of "elder brethren" in the faith of Abraham.
This is referred to the general priesthood of the people. Not the priestly ministry that only Aaron and his sons; then men from the tribe of Levi had to perform by certain rites and vestments as ordained by God.
64 Through the prophets, God forms his people in the hope of salvation, in the expectation of a new and everlasting Covenant intended for all, to be written on their hearts.22 The prophets proclaim a radical redemption of the People of God, purification from all their infidelities, a salvation which will include all the nations.23 Above all, the poor and humble of the Lord will bear this hope. Such holy women as Sarah, Rebecca, Rachel, Miriam, Deborah, Hannah, Judith and Esther kept alive the hope of Israel's salvation. the purest figure among them is Mary.24
In the O.T. God had to do a covenant with Abraham, then with Moses more than once for the people of Israel kept breaking it. But the Last and permanent Covenant is fulfilled with our Lord Jesus Christ and His Church.
John 3:27; John 15:5; Matthew 19:26