Peter and John were called by the Lord to be His disciples. Later they were appointed as apostles directly by the Lord and were listed among the twelve apostles.
Although Paul and Barnabas were not disciples of the Lord while He was on the earth, they were apostles constituted directly by the revelation of the Lord. This is especially clear in the case of Paul. His being an apostle was not something set up by men; rather, he was directly appointed by the Lord. The gospel and truth that he preached was not learned from men nor taught by men, but came directly from the Lord’s revelation. Before he was saved, he was called Saul. He was born and raised in the city of Tarsus of Cilicia. He was trained according to the strictness of the law of the fathers at the feet of Gamaliel and was zealous for God. He persecuted the believers of the Lord unto death, binding and delivering to prison both men and women (Acts 22:3-4). One day, while on his way to Damascus to bind the disciples, a great light shined out of heaven around him, and he fell to the ground and heard a voice saying, “Saul, Saul,...I am Jesus the Nazarene, whom you are persecuting....Rise up and go into Damascus, and there it will be told you concerning all things which have been appointed for you to do” (Acts 22:7-10). The Lord called him and appointed him to be an apostle to the Gentiles from that day on. Later the Lord showed him directly various visions and revelations concerning God’s New Testament economy.
We can find only one case of this kind of apostle in the Bible, Apollos. In 1 Corinthians 4:6 and 9 we see that Apollos was also an apostle. Paul first mentioned “us,” which includes him and Apollos, as being among the brothers. Then he said that God had set forth “us the apostles” last of all. According to the context, Apollos was one of the apostles whom Paul referred to. Hence, Apollos was also an apostle. Although he was raised up by the Lord, his knowledge of the Bible was learned from others. When he expounded the Scriptures, he was powerful, but he was not clear concerning the way of the Lord. He needed the further perfecting of Aquila and Priscilla. For this reason, he was not an apostle constituted directly through the Lord’s revelation, but was one perfected by others through learning.
Timothy and Silas were two apostles perfected by the Apostle Paul. During his second journey, Paul chose Silas. Later he also took Timothy along with him (Acts 16:1-3) for the Lord’s work. As a result, they became apostles under Paul’s leadership and worked together with Paul.
If we compare the Apostle Paul’s word to Titus in Titus 1:5-9 with his word to Timothy in 1 Timothy 3:1-7, we can see that Titus was probably an apostle produced by Paul.
In the New Testament, we read of no other kind of apostle than these three kinds; there is no fourth kind. Although in 2 Corinthians 8:23 there is a reference to two apostles of the churches, these were men merely sent by the churches to conduct business for the churches; they cannot be considered under the three kinds of apostles listed above.