And his mother and his brothers came, and standing outside they sent to him and called him. And a crowd was sitting around him, and they said to him, “Your mother and your brothers are outside, seeking you.” And he answered them, “Who are my mother and my brothers?” And looking about at those who sat around him, he said, “Here are my mother and my brothers! For whoever does the will of God, he is my brother and sister and mother.”
Mark 3: 31-35 ESV
Again and again we can see a pattern in the people around Jesus at that time. There are 2 groups of people, one group is the one who understand or believe in Jesus and they’re inside trying to get close to Jesus. While the other group is the one who do not understand or do not believe in Jesus, they’re always outside this group. In this part of the passage, ironically it’s Jesus’ family who’re outside, they’re not part of the people who sits around Jesus to hear what he’s teaching about.
On top of that we can see from the previous passage that Jesus family (Mary and Jesus’ brothers) didn’t think that Jesus is sane. Therefore it’s obvious that they’re not really here to come and listen to Jesus’ teaching, instead they’re coming to seize him. In contrast the people inside Jesus’s inner circle, are the one who believes and trust in His teaching and willing to do the will of God. That’s why what Jesus said made sense, Jesus’ true family are the people who does the will of God!