Answer: The Scriptures indicate that there were to be twelve Apostles – no more and no less. Following are a few Scriptural proofs:

• Matthew 10: 1-4 and Luke 6: 13-16 give the account of their appointment by Jesus.
• Jesus said to His Apostles that in His Kingdom they would “sit upon twelve thrones, judging the twelve tribes of Israel” (Matthew 19: 28) (Luke 22: 29, 30).
• In Revelation 21: 10, 14, heavenly Jerusalem is said to be built upon “twelve foundations, and in them the names of the twelve apostles of the Lamb.”

In Jesus’ last meeting with His disciples before His ascension, He asked them to tarry at Jerusalem until they would receive the promised power from heaven (Luke 24: 49). According to the account in Acts 1: 12-26, the disciples returned to Jerusalem and continued in prayer. Then Peter stood up and reminded them of David’s prophecy in Psalm 109: 8, that someone would need to replace Judas as an Apostle, and that whoever he would be, he would have to be a witness of Jesus’ resurrection (verse 22). Two candidates were put forward – Barsabas (surnamed Justus) and Matthias. After prayer the disciples cast lots and Matthias was selected.

Nothing more is heard about Matthias, one indication that the disciples had erred in attempting to replace Judas themselves. Their mistake is understandable, however, in light of the fact that they had not yet been anointed with the power of the holy spirit which came upon them at Pentecost, and they perhaps did not fully recognize that only God, through Jesus, has the authority to appoint an Apostle.

The Lord merely ignored their selection, and in His own due time, appointed St. Paul to replace Judas as the twelfth Apostle. The account of his conversion is found in Acts 9: 1-30. Following are some Scriptural proofs of his Apostleship:

• The Lord said of him: “He is a chosen vessel unto me, to bear my name before the Gentiles, and kings, and the children of Israel” (Acts 9: 15).
• Paul testified to his having witnessed the resurrection of Jesus, and how God’s grace had blessed his ministry as an Apostle (Acts 26: 16-18) (1 Corinthians 9: 1) (1 Corinthians 15: 5-11).
• Paul found it necessary to defend his Apostleship against critics, humbly arguing that he was not one whit behind the very chiefest apostles in anything (2 Corinthians 11: 5) (2 Corinthians 12: 11).
• Paul opens nine of his epistles by referring to himself as “an apostle” (Romans 1: 1) (1 Corinthians 1: 1) (2 Corinthians 1: 1) (Galatians 1: 1) (Ephesians 1: 1) (Colossians 1: 1) (1 Timothy 1: 1) (2 Timothy 1: 1) (Titus 1: 1).
• The majority of the New Testament was written by Paul.  

‍