“when his family heard it.” The Greek is idiomatic: literally, “those who were beside him,” but that is an idiom that generally refers to friends, family, or associates, and here the context favors Jesus’ family (cp. Mark 3:31). The Greek is para (#3844 παρά), a preposition usually meaning “beside.” Thus the book of Mark is vague here, saying only that these people were those who were beside him. This is a case when we have to rely on other parallel records to give the details, and we learn what happened from the scope of Scripture. Matthew 12:46 and Luke 8:19 let us know that this group of people is his mother and brothers. At this point, Jesus’ brothers did not believe in him (John 7:5) and thought he was out of his mind. It is not clear what Mary thought. Given the way Jesus said, “Who is my mother” (Matt. 12:48), it is possible and perhaps even likely that, although Mary knew Jesus was the Messiah, she was confused about him and thought that he had somehow gotten away from what he was supposed to do as Messiah. The common teaching of the day about the Messiah was wrong, for example, that he would never die. It is also possible, however, that with her husband dead she was not able to stand against her sons who would have been running the family at the time.
This record of Jesus’ family coming to take charge of him is a clear indication that Jesus’ step-father, Joseph, was dead, otherwise he would have been leading the group. That means Joseph died between the time Jesus was 12 (Luke 2:42) and the time he started his ministry. He had worked with his father, the carpenter, and had become a carpenter himself (Mark 6:3). This group “set out” to take him. They arrive in verse 31.
“to seize him.” In the honor-shame society of the ancient Near East, if a family member was behaving in such a way that the family thought he or she was bringing shame to the family, members of the family would seize the offending person and take physical charge of him. Women were sometimes killed for dishonoring the family, and this is still known today as “honor killing.” Jesus was in a precarious situation if his family had won the crowd, but as it turned out (and we are not told exactly how this occurred) his family left without taking him with them.