From The Gospel of Mark, by Mary Healy, commenting on Mark 6:7-13
In the Jewish tradition of hospitality (see Gen 18:1–8; 19:1–3; Job 31:32), it was common for travelers to be welcomed spontaneously into homes along their way, especially since not every village boasted an inn. Jesus instructs the Twelve to stay in whatever house they enter, not moving about from house to house.
The reason may be to avoid any rivalry or jockeying for prestige that could arise among villagers wishing to host them. Nor may the apostles upgrade their accommodations. Like Jesus, they were likely to be besieged by crowds once they began the ministry of healing and exorcism in a given town (see Acts 8:6), and staying in one place would limit unnecessary distractions.
The stakes involved in accepting or refusing the gospel are high. Jesus equates the response given to his apostles with a response to himself (see 9:37). To welcome them is to welcome him. And to refuse to listen is to forfeit his invitation to eternal life (see 8:38; 16:16; John 3:18).
To shake the dust off one’s feet was a symbolic gesture of repudiation (Acts 13:51), meant as a solemn warning to those who rejected the apostles’ message. For Jews, the soil of Israel was holy (see 2 Kings 5:17; Isa 52:2); upon reentering the land after a journey they would shake the pagan dust off their feet as a sign of separating themselves from Gentile ways. This gesture would serve as a testimony against such unreceptive villages on the day of judgment. It is also a reminder to the apostles not to be discouraged by the resistance they will sometimes encounter. Their job is to carry out their mission obediently; success is in the hands of God. No one can be compelled to accept their message.
Mark describes the apostles’ preaching in the simplest of terms: like John the Baptist (1:4), they preached repentance (metanoia), the call to turn away from sin and toward God in a complete change of heart. The fullness of the Christian gospel, the victory of the crucified and risen Lord, can be proclaimed only after the resurrection. But their message, like that of Jesus, carries authority (6:7); it is accompanied by works of power that serve as visible signs confirming its truth.