Matthew begins his account of the Good News with these words: "An account of the genealogy (or birth) of Jesus the Messiah, the son of David, the son of Abraham." The first chapter ends with Joseph naming the child Jesus, as he had been told to by the angel who appeared to him in a dream. By naming the child, Joseph, a descendant of David, claimed for Jesus that same lineage.
But son of Abraham is another matter. John the Baptist would later challenge those who heard his preaching but did not take it to heart: "Do not presume to say to yourselves, ‘We have Abraham as our ancestor’; for I tell you, God is able from these stones to raise up children to Abraham." To be a child of Abraham is to be the inheritor of a promise: "I will indeed bless you, and I will make your offspring as numerous as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of their enemies, and by your offspring shall all the nations of the earth gain blessing for themselves, because you have obeyed my voice." All the nations of the earth are to be blessed by the offspring of faithful Abraham.
To make that point perfectly clear, Matthew goes on in chapter two to tell the story of the Magi, who are not descendants of Abraham, but are foreigners, gentiles, and who come to Bethlehem to worship and to be blessed. In this holy Child will God's promise to Abraham. In this Child will all the peoples of the earth find blessing. Sadly, the Church has far too often claimed the blessing only for itself. Far too often we have hid the Light, not under a bushel basket, but behind walls of prejudice and arrogance and triumphalism. Far too often we act as if the Church was in business to serve us, rather in the business of serving others, of proclaiming and spreading the reign of God, of being a blessing to all the nations of the earth. The promise to Abraham means that the nations have a claim on us, have a right to expect that through us they will receive God's blessing.
When Jesus began his ministry, Matthew tells us that his first sermon was simple: "Repent, for the kingdom of heaven has come near." The reign of God has begun and we are called to repent and become a blessing.