What does Mark 3:34 mean?
Biological families, and intense loyalty to those bloodlines, are the building blocks of a patriarchal society. Order, safety, provision, and honor are all tied to the family. Jesus turns this cultural presumption upside-down.The terminology of family is widespread throughout the New Testament church. The book of Acts uses the term "brothers" in more than twenty verses, very few of which are speaking about biological family. Their context is that of the spiritual family of the church. In Romans, Paul calls the believers who live there "brothers" even though he's never met them. He tells Timothy to treat church members as fathers, brothers, mothers, and sisters (1 Timothy 5:1–2).
This is the second time in this chapter Jesus has "looked around" the synagogue at the people, sitting and listening. The first is in Mark 3:5 when He looks over the Pharisees who watch to see if He will heal a man on the Sabbath. His reaction to the Pharisees' hard hearts is anger and grief. Now, in a packed room in a packed house, Jesus looks around and sees the people there as a spiritual "family." They aren't waiting for Jesus to slip up. They aren't conspiring against Him. They don't think He's an embarrassment. They just want to listen to what He has to say, and absorb the truth.
Just as Jesus redefines family, He redefines religious community. Mark mentions only one more time when Jesus will teach at a synagogue. It will be in Nazareth, His home town, and He will be soundly rejected (Mark 6:1–6).
Gatherings are important in the life of a church. If those gatherings happen to fall in the same place at the same time each week, that's great. But it isn't the building or the ceremony that makes a church. It's the group of people who come to learn about God, worship Him, and obey Him. They may meet in a designated building, a home, the seashore, or a mountaintop. The same qualities that define a godly church also describe the family of God: faith in Christ (John 1:12; Galatians 3:25–29) and obedience to God (Mark 3:35).