What does Mark 3:35 mean?
Jesus shows us the tension which occurs when a parent's wish contradicts God's will. Jesus will not follow Mary back to Nazareth, but He does believe in honoring one's parents. Although He warns that it is sometimes necessary to leave family for the sake of the gospel (Mark 10:28–30), He also teaches that taking care of parents is an essential part of worshiping God (Mark 7:9–13). Jesus exemplifies this responsibility. While hanging from the cross, He makes sure Mary was cared for (John 19:26–27).Eventually, Mary and at least two of Jesus' brothers join His spiritual family. James becomes the leader of the church in Jerusalem and writes the book James. Judas writes the book Jude. Although Jesus has to leave them for a time, geographically, relationally, and spiritually, they are welcomed into the body of believers.
The passage says Jesus' family is comprised of those who do God's will. The first and most important point of obedience is believing in Christ. Having faith that Jesus is the Son of God who died for our sins and was raised again gets us in to God's family. Obeying God in other areas gives evidence that we are in God's family (James 1:22; 2:18) and makes the family much more peaceful (Ephesians 4:1–6).
It should provide us hope that some staunch believers rejected Jesus at first, as did Paul (Acts 8:1–3). Others believed timidly, like Jewish council-member Joseph of Arimathea (John 19:38). But God can, and does, change minds. All are welcome in God's family, and the angels respond with joy when they come (Luke 15:10).
Finally, it is significant that Jesus includes "sister." He has many women among His disciples (Luke 8:1–3), and even more go on to build the church (Acts 16:14–15; 1 Corinthians 16:19; Colossians 4:15). Galatians 3:28 says, "There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus." Women are an essential part of any family, including God's. Jesus' deliberate inclusion of women is, for that time period, highly unusual.