In this […] Gospel, Jesus takes the initiative of sending the Twelve Apostles out on mission (cf. Mk 6:7-13). In fact the term “apostles” means, precisely, “messengers” or “envoys”. Their vocation was to be fully achieved only after Christ’s Resurrection with the gift of the Holy Spirit at Pentecost. Yet it is very significant that Jesus wants to involve the Twelve in his action from the outset: it is a sort of “apprenticeship” with a view to the great responsibility that awaited them. The fact that Jesus calls certain disciples to collaborate directly in his mission demonstrates one aspect of his love, namely, he does not spurn the help that other people can contribute to his work; he knows their limitations, their weaknesses, but bears no contempt for them. On the contrary Jesus confers on them the dignity of being his envoys. He sends them out two by two and gives them instructions which the Evangelist sums up in a few sentences. The first concerns the spirit of detachment: the Apostles must not be attached to money or to other comforts. Then Jesus warns the disciples that they will not always receive a favourable welcome. Sometimes they will be rejected; they might even be persecuted. However this must not frighten them: they must speak in Jesus’ name and preach the Kingdom of God without being worried about whether or not they will succeed. Succeed — its success must be left to God [...].
Jesus warns the Twelve that in some places they may be rejected. Should this be the case, they are to go elsewhere, having shaken the dust from their feet in public. This sign expresses detachment in two senses: moral detachment — as if to say it is you who have refused the proclamation offered to you — and material detachment. We did not seek and do not want anything for ourselves (cf. Mk 6:11).
The other very important instruction in the Gospel passage is that the Twelve must not be content with preaching conversion. They must accompany their preaching, in accordance with Jesus’ instructions and example, with care for the sick, with caring for those who are sick in body and in spirit. It speaks of the healing of illnesses and also of driving out demons, that is, of purifying the human mind, cleansing, cleansing the eyes of the soul that are clouded by ideologies and hence cannot see God, cannot see truth and justice. This twofold corporal and spiritual healing is always the mandate of Christ’s disciples. Hence the apostolic mission must always include the two aspects of preaching God’s word and of showing his goodness in gestures of charity, service and dedication.
[Pope Benedict, Frascati homily 15 July 2012]