1 Then he called his twelve disciples together, and gave them power and authority over all devils, and to cure diseases.
2 And he sent them to preach the kingdom of God, and to heal the sick.
3 And he said unto them, Take nothing for your journey, neither staves, nor scrip, neither bread, neither money; neither have two coats apiece.
4 And whatsoever house ye enter into, there abide, and thence depart.
5 And whosoever will not receive you, when ye go out of that city, shake off the very dust from your feet for a testimony against them.
6 And they departed, and went through the towns, preaching the gospel, and healing every where.
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Jesus is truly a Teacher: He alternates "theoretical instruction" for His disciples with "practical lessons." In fact, they spend only three years with their Mentor, receiving from Him everything they are able to receive, and then they will have to carry the Gospel and preach the Kingdom of God throughout the whole world. While they are still learning, they must taste the mission, see how the word of God acts in the world, how evil retreats, how the eyes of people who receive the Good News light up. Later, after Christ's Ascension, they will receive the gift of the Holy Spirit and accept a special power for witness to Christ, but already now Jesus equips them with everything needed for preaching: instructions, and "power and authority over all demons and to cure diseases."
Mission is service, so the messengers must not display worldly power or wealth; they are called to rely on God in everything. Their task is to bring the message, not to persuade or force people to accept it, and the healing of the sick is not a bright show meant to attract unbelievers, but simply a nonverbal witness that the Kingdom of God has drawn near.