Four were fishermen—the brothers Simon Peter and Andrew and another set of brothers, James and John. Philip and Bartholomew are often mentioned together. Matthew was a publican, or tax collector. The other five were Thomas, Thaddeus, James the son of Alphaeus, Simon Zelotes, and Judas Iscariot. Jesus gave the apostles a charge to go and preach of the kingdom of heaven and to perform miracles in His name, to heal the sick, cleanse the lepers, raise the dead and cast out devils. He gave them power to do these things and commanded them to rely solely on Him to provide the necessities of life as they went among the people (Matthew 10).
They were told that they would be tried and tested, but should always rely on the Spirit in all that they would say and do. They were counseled to remember that the power by which they spoke and performed miracles was not of their own making, but of the One who had sent them, Jesus Christ. He told them that they must give up all else, even their families, if need be, to follow Him (Mark 6:7-13; Luke 9, 12, 14:25-28). The Doctrine and Covenants emphasizes that the Twelve are to be those who take upon them the name of Christ with full purpose of heart (Doctrine and Covenants 18:28-32; 37-38). If they will do this, His grace is sufficient for their needs and desires.
When Judas Iscariot died, Matthias was appointed to the apostleship (Acts 1:15-26). Paul also spoke of himself as an apostle (Romans 1:1; 1 Corinthians 1:2; 9:1; Galations 1:1). Furthermore, Paul spoke of James, the brother of Jesus Christ, and of Barnabas as apostles (Galations 1:19; 1 Corinthians 9:5-6). These men also served as emissaries of Jesus Christ in preaching His gospel and in serving the saints of His Church.
After the resurrection of Jesus, the ancient apostles of Jesus Christ were given a great commission on a mountain of Galilee. Jesus reaffirmed their first charge given when they were called. They were commanded to go and teach all nations, to baptize in the name of the Father, Son, and Holy Ghost, and to continue to teach every person who would listen, all that Jesus had taught them. They were given the promise that He would always be with them and would give them power to perform mighty miracles in His name (Matthew 28:16-20; Mark 16:15-18). “And whosoever shall believe in my name, doubting nothing, unto him will I confirm all my words, even unto the ends of the earth” (Mormon 9:22-25).