This passage from Mark's gospel is something of a puzzle and unfortunately and not infrequently gives rise to anti-Marian explanations and sentiments. As a fervent Jew and as the Son of God, Jesus would have kept the Fourth commandment and would never have resorted to any rejection of His Mother.
If we fit the passage into the whole range of information about Jesus given us in the Gospels, one wonderful human characteristic of Jesus was his very highly-developed imagination which he used so effectively in his preaching of the kingdom. Simple every-day things like a farmer sowing seed gave rise to striking and well-remembered parables.
So the story about Jesus' reply when he was told that his mother and relatives were outside wanting to see him gave rise to a straightforward but eternally challenging short parable on Jesus' lip.
In the Kingdom of God, it is not blood relationships that is paramount but doing the will of God. It is this that is significant and determinative of our belonging to Jesus. Unfortunately, like many human societies guided by merely social concerns, the Church has in its history not always been free from the scourge of nepotism and similar favour-bestowing tendencies and practices. For a civilized society which put in such practices, these words of Jesus would be more reminiscent of the justice of God's kingdom.
Lord Jesus, through Your saving grace, grant that Your Father's will be done in our lives as it is in heaven.