What is an apostle?
Here's the answer:
An apostle is someone who was sent out by the Lord.
Within the Bible, there are two meanings behind the word apostle. One of the meanings directly refers to the 12 disciples of Jesus, who are also called the 12 apostles. Another meaning refers to those who are sent out to be messengers of Jesus.
The 12 apostles were the first people to share the Good News with others after Jesus' had risen from the dead. They were very important to the development of the church and teaching people about Jesus. The qualifications of this type of apostle were: (1) to have been a witness of the resurrected Christ (1 Corinthians 9:1), (2) to have been chosen by the Holy Spirit (Acts 9:15), and (3) to have the ability to perform signs and wonders (Acts 2:43; 2 Corinthians 12:12). This specific office of apostle cannot be held today.
Beyond the twelve apostles of Jesus Christ, there were also apostles in a generic sense. For example, Paul and Barnabas are referred to as apostles. This kind of apostle was like a missionary who was sent out to tell others about Jesus.
Even though some people are sent out today, it is best not to use the title apostle.
"Here are the names of the 12 apostles. First there were Simon Peter and his brother Andrew. Then came James, son of Zebedee, and his brother John. Next were Philip and Bartholomew, and also Thomas and Matthew the tax collector. Two more were James, son of Alphaeus, and Thaddaeus. The last were Simon the Zealot and Judas Iscariot. Judas was the one who was later going to hand Jesus over to his enemies" (Matthew 10:2-4).
"While they were worshiping the Lord and fasting, the Holy Spirit spoke. 'Set apart Barnabas and Saul for me,' he said. 'I have appointed them to do special work'" (Acts 13:2)