If there were only 12 apostles, why does the Bible refer to Barnabas as an apostle in Acts 14:14?
This is a good question and one which deserves to be answered. Let's notice the text about which this question is raised: "Which when the apostles, Barnabas and Paul, heard of, they rent their clothes, and ran in among the people, crying out...." (Ac. 14:14). Perhaps the confusion arises as the result of failing to understand how the word "apostles" is used in the Bible. So let's take a look.
The word "apostle" is used in both the singular and plural forms in the Bible. This word was translated from the Greek word apostolos. It is a word which means, according to Strong: "A delegate; specially, an ambassador of the Gospel; officially a commissioner of Christ." Apostolos occurs 81 times in the King James Version. It has been rendered "apostle" 78 times, "messenger" 2 times, and "he that is sent" 1 time. "Apostle" in the Bible can be applied in both a limited sense as well as a general sense.
While on Earth, Jesus hand selected men who would accompany him during this three year ministry. A list of their names is given in Matthew 10:1-4. Notice in verse 5 the text says: "These twelve Jesus sent forth...." Luke recorded: "And when it was day, he called unto him his disciples: and of them he chose twelve, whom also he named apostles" (6:13).
These 12 were sent on the Limited Commission (Mt. 10:5-15). It was limited in that they were not to go into the way of the Gentiles nor into any city of the Samaritans but rather to the lost sheep of the house of Israel (vs.5,6). They were sent on the Great Commission (Mt. 28:18ff; Mk. 16:15ff). This was an unlimited commission in the sense they were to go to all nations and preach to every creature.
Judas, one of the original 12 apostles, fell by transgression as he betrayed the Lord and was replaced by Matthias (Ac. 1:15-26). This brings the number to 13 who were chosen to be Apostles. Saul of Tarsus, to whom the Lord appeared (Ac. 9:1-9), was "called to be and apostle, separated unto the gospel of God" (Ro. 1:1). Paul was an apostle to the Gentiles (Ga. 2:7,8). This brings the total number of men chosen to be apostles to 14. These men were apostles in a limited sense in that they were selected for a particular work and sent forth for that purpose. They also qualified as such of which no man today can qualify. Notice: "Wherefore of these men which have companied with us all the time that the Lord Jesus went in and out among us, Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection" (Ac. 1:22,23). Did you catch the qualifiers? One must have been a witness of the resurrected Jesus in order to have been an apostle in this limited sense. No man today can lay claim to meeting this qualification.
As the word "apostle" is used in a limited sense, it is also used in a general sense. Keep in mind the word refers to one who has been sent. Notice how this word has been rendered and applied to others in the New Testament. Paul penned: "Whether any do enquire of Titus, he is my partner and fellowhelper concerning you: or our brethren be enquired of, they are the messengers [apostolos] of the churches, and the glory of Christ" (2 Cor. 8:23). Paul, writing to the church at Philippi concerning Epaphroditus: "Yet I supposed it necessary to send to you Epaphroditus, my brother, and companion in labour, and fellowsoldier, but your messenger [apostolos], and he that ministered to my wants" (Ph. 2:25). Again, in this text, Epaphroditus is referred to by the same original word from which "apostle" is rendered. Yet, he was not an apostle in the specific or limited sense but rather in the general sense.
Back to the original question: Why does the Bible refer to Barnabas as an apostle? Now that we know "apostle" can refer to one who has been sent read Acts 13:1-3 in light of that fact: "Now these were in the church that was at Antioch certain prophet and teachers; and Barnabas, and Simeon that was called Niger, and Lucius of Cyrene, and Manaen, which had been brought up with Herod the tetrarch, and Saul. As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them. And when they had fasted and prayed, and laid their hands on them, they sent them away."
Barnabas was sent with Paul to the work of preaching the Gospel and as a result is referred to as an apostle. He was an apostle in the general since of being sent. This is a great question and one which reminds of the importance of words and studying their meaning, the context in which they are found, and the ways they are used in the other passages.