Jesus Ordains the Twelve by the SeaBible World

Mark 3:15

And to have power to heal sicknesses, and to cast out devils:

Mark 3:15 belongs to the calling of the twelve to the apostolate on a mountainside a little distance from the Sea of Galilee, beneath sheltering trees, where the sermon on the mount was also given. With no costly sanctuary at command, Christ led them to the retreat He loved, withdrawing from the confusion of the city to the quiet of the fields and hills, for the fields and hills were His favorite resorts and much of His teaching was given under the open sky rather than in temple or synagogues. He chose those open groves because they were more in harmony with the lessons of self-abnegation He desired to teach, because no synagogue could have received the throngs that followed Him, and because He loved the scenes of nature so that to Him each quiet retreat was a sacred temple. The sacred experiences of that day were forever linked in their minds with the beauty of mountain and vale and sea. That ordination was the first step in organizing the church that after His departure was to be His representative on earth.

The verse commissions the twelve to the apostolate and to the sacred work of the gospel by giving them power to heal sicknesses and to cast out devils and demons. They were chosen to learn from Him, to witness His works, and to receive His instruction so they could be equipped for gospel work like His own, to teach and to heal the sick and confront demons. They were thus prepared to go out on their own to teach and work as He did, to continue the work after His death, both while He was with them and after His death.

The choice shows His training of humble men for the work they would carry forward after He left, connecting them with Himself to educate them for service, choosing men who would obey and remain faithful, which did not show a preference for ignorance. The wider choosing shows selection of men of diverse character whose differences could complement one another and help them carry out the work together. Even Judas received this authority to heal the sick and cast out devils and a place among the twelve for work as an evangelist, though he did not fully surrender to Christ or give up worldly ambition and love of money. After their ordination, Jesus healed the sick and comforted the sorrowing.