At one point in his ministry, Jesus was teaching with a large group of people crowded around him. His family expresses worry about him, since the news about him has gone far and wide, and the religious authorities from Jerusalem are spreading the word that he is possessed by the Devil. So they find out where Jesus is and call for him. Someone tells him the news: Look, your mother and your brothers are outside looking for you (Mark 3.32).
Jesus' response is significant. He says: Who is my mother, or who are my brothers? And looking around at the people gathered in a circle around him, he responds, Behold, these are my mother and my brothers. Anyone who does God's will is my mother and brother and sister (3.33-5).
Now these people gathered Jesus are not particularly holy or special individuals in any moral sense. They are ordinary Joe Schmo-types, like you and me. They have weaknesses, shortcomings, failings, vices, histories. Yet Jesus heaps tremendous words of honor on them, saying that they do God's will and that they are his brothers and sisters and mothers. Imagine that—to be a part of the family of God's Son!
What did they do that was so great, so as to deserve such honors? Nothing in particular except this: they came to listen to the word of Christ. This is God's will, that ordinary folks such as us sit and listen and learn from the Son of God. When we do this, we are a part of God's family and we can call Jesus our brother.