Matthew 12 - IVP New Testament Commentaries
Jesus' True Family
If you have ever felt like the whole world was against you, you can at least empathize with some of the pain of Jesus' calling: not only the religious leaders (vv. 24, 38) but his own family doubted him. Family ties were paramount (compare clan ties even in Rome-for example, Dupont 1992:106-8), and being perceived as antifamily brought even more reproach then than it does today (see Derrett 1973:39). Yet Jesus followed the practice he had demanded of others (8:21-22; 10:37): the kingdom of God comes first. Obedience to God's will (7:21; 21:31; 26:42) is what makes one Jesus' true brother, sister or mother (25:40; 28:10). When we acknowledge God as our Father, his family becomes our family, and our allegiance to him as Father must come before all earthly allegiances.
From this we learn both the importance of obedience and the futility of depending on other means of access to Jesus. Those who suppose they have some natural claim on the kingdom have no claim on it at all. But those who obey God's will for themselves have an intimate relationship with Jesus and can depend on him the way members of his immediate family can. Perhaps Jesus stresses the priority of spiritual family here because he hopes to be able to count on his disciples too.