While he was still speaking to the crowds, his mother and his brothers appeared outside, wishing to speak with him. (Someone told him, "Your mother and your brothers are standing outside, asking to speak with you.") But he said in reply to the one who told him, "Who is my mother? Who are my brothers?" And stretching out his hand toward his disciples, he said, "Here are my mother and my brothers. For whoever does the will of my heavenly Father is my brother, and sister, and mother." (Mt 12:46-50)
Jesus was busy in his mission. He was speaking to the crowds. He was ready to be disturbed by any. For him his ministry was more important. He did not want to be moved away from the people for who he was sent. He wanted to continue his mission and carried it on without being disturbed. He was single focused. Establishing the kingdom was his mission.
Mother and brothers wanted to talk to him. We do not know the urgency of their coming. The author has not said anything about that, If they wanted to interrupt him then there should have been something very urgent. But Jesus was very clear about his mission and he was sure that not even his mother and the close relations should come in between him and his mission.
He beautifully gives the reason for such an attitude as saying that whoever does the will of the father in heaven is his mother and relations. His relationship is based on God and doing His will. When Jesus was in his ministry nothing mattered to him except God and doing the will of the Father. And anyone who was interested in doing the will of the father was his relation.
