"Jesus went up on a mountainside and called to him those he wanted, and they came to him. He appointed twelve - designating them apostles - that they might be with him and that he might send them out to preach and to have authority to drive out demons." NIV translation
Jesus called twelve of His disciples and set them apart as apostles. His purpose for designating them had three parts. As apostles, they were allowed to be with Him constantly to see and to hear His teaching. At this time, the crowds were getting rather large but these men were granted access at all times. The second part is that their purpose was to preach the gospel about Him and they would be the ones to travel to other parts of the world on His behalf. The third part was to demonstrate His power and authority by driving out the demons. At this time, the demons had been coming and falling down before Him but, when He was gone, they were not just going to leave on their own.
It is interesting to note that He designated twelve and we remember that the number is associated with divine spiritual authority. There are many today who are using "apostle" as a title but that is clearly not what Jesus meant for us to do.
"These are the twelve he appointed: Simon (to whom he gave the name Peter); James son of Zebedee and his brother John (to them he gave the name Boanerges, which means Sons of Thunder); Andrew, Philip, Bartholomew, Matthew, Thomas, James son of Alphaeus, Thaddaeus, Simon the Zealot and Judas Iscariot, who betrayed him." NIV translation
What an unlikely group of men to pick for such an important mission. All of these men (except for one) were simple fishermen with no big formal education. The exception was Matthew who was considered to be lower than fishermen as he had been a tax collector. Though Jesus has not designated us as apostles, He has given us the same mission that He gave these men. Many people want to argue about the reasons that God chose these men but the simple fact of the matter is that He knows all men and He knows all of the plan. That is how He could choose Judas who would be the one to betray Him unto death.
"Then Jesus entered a house, and again a crowd gathered, so that he and his disciples were not even able to eat. When his family heard about this, they went to take charge of him, for they said, 'He is out of his mind.'" NIV translation
The crowds followed Him everywhere in search of physical healing. We see, here, that His family accused Him of being crazy and wanted to get Him and hide Him away. This is a reminder that many without faith see our faith as craziness. That is what was happening to Jesus and it happens even today. The simple fact of the matter is that those without faith cannot understand the actions of a Christian.