Whoever does the will of God is my brother and sister and mother. Among the many accusations that were labeled against Jesus is what others might have interpreted as Jesus' attempt to reconstitute the family judging from his behavior or statements. The family was a very essential social unit in the culture of Jesus' community.  The family was considered a sacred institution for not only did it give an individual his/her identity, but it also guaranteed his/her place in the larger society. A family guaranteed kinship. It was kinship that guaranteed Israel as a nation both its future and place in the world because everything " Israel" was imparted to an individual from the family. As such, one was bound to the family by ties that could never be broken. It must have come as a shock, then, to the mother and brothers of Jesus when they heard him utter words that were closest to denouncing his family.
When Jesus gestured towards those who were gathered about him and said that they were his family, he was not denouncing his family. From what can be gleaned from the Gospel accounts, it is safe to assume that Jesus appreciated and treasured the traditions of his community (he was always in the synagogue on the Sabbath, and he was also present together with his mother at the wedding in Cana). He must have appreciated his people's understanding of the family unit and how it functioned (as he hung on the cross dying, he placed his mother under the care and protection of the beloved disciple). Jesus saw in the tradition of his people some inherent good that he wished to be "unlocked" and shared with the entire world. He understood that Israel as a people had been elected by God to be a means of extending God’s blessing and salvation to the entire world. Part of being a blessing to the nations, Jesus believed, was Israel opening up herself and inviting others to share in her life and tradition (in the words of Moses, there was no other nation under the earth whose statutes and decrees were as just as Israel’s [cf. Deuteronomy 4:8]). Jesus saw in his community’s understanding of the family something that would be instrumental in his ushering in of the Kingdom of God. And he wanted to extend this understanding to the nations.
When Jesus' mother and brothers come looking for him, Jesus utilized the opportunity to invite the crowd to re-think their understanding of the family. Instead of restricting kinship to blood relations, Jesus presented to them a new understanding of kinship that extends to the entirety of creation. In this new understanding, one’s family becomes constituted of whoever lives according to the will of God. Mary obviously was a doer of God's word (her response to the angel of the Lord was: ‘behold I am the handmaid of the Lord, may it be done tome according to God’s will’), as were the people gathered about Jesus as they listened to him. Jesus' family is thus constituted by doers of the will of God, those who constitute the kingdom of God.