Jesus Chose the Twelve

"And He went up on the mountain and called to Him those He Himself wanted.
And they came to Him.
Then He appointed twelve, that they might be with Him and that He might send them out to preach, and to have power to heal sicknesses and to cast out demons."
Mark 3:13-15

"Then Jesus went about all the cities and villages, teaching in their synagogues, preaching the gospel of the kingdom and healing every sickness and every disease among the people.
But when He saw the multitudes, He was moved with compassion for them, because they were weary and scattered, like sheep having no shepherd.
Then He said to His disciples, 'The harvest truly is plentiful, but the laborers are few.
Therefore pray the Lord of the harvest to send out laborers into His harvest.'
And when He had called His twelve disciples to Him, He gave them power over unclean spirits, to cast them out, and to heal all kinds of sickness and all kinds of disease."
Matthew 9:35-10:1

Paying close attention to the sequence.
Jesus said that the harvest is plentiful, but the laborers are few and to pray the Lord of the harvest to send out laborers into His harvest.

Then we see Jesus, the Lord of the Harvest, sending out laborers into His harvest; His disciples.

He sends them to heal all kinds of sicknesses and all kinds of diseases, and cast out devils.
This is what He sent them out to do.