Why are there differences in the four lists of the disciples?

Question

Answer

There are four lists of the disciples found in the Bible — one each in Matthew, Mark, Luke, and Acts. Though the ordering in some cases may differ, the lists are essentially the same. Matthew, Mark, and Luke contain a list of twelve disciples, while the book of Acts contains only eleven, which is because Judas Iscariot committed suicide after betraying Christ. He was later replaced by Matthias (Acts 1:21-26). Thaddaeus (Matt. 10:3; Mark 3:18), the disciple with many names, and Judas the son of James (Luke 6:16; Acts 1:13) are the same individual:

The name Thaddaeus (meaning "large hearted") appears in the list of disciples given in Matthew 10:3 and Mark 3:18, between James and Simon. Luke does not include him in either of his lists (Luke & Acts); but Luke includes Judas the son of James (Luke 6:16; Acts 1:13). The two names - Thaddaeus and Judas the son of James - never appear in the same book. So, this adds credibility to the fact that the two names refer to the same person. Because of the treasonous act of Judas Iscariot, the name "Judas" was probably unpopular (it's last in 3 lists and not in the 4th) so this may be the reason for Judas the son of James alternate names (Thaddaeus, Lebbaeus, etc.). The Pulpit Commentary states, "There is no doubt that Lebbaeus and Thaddaeus were surnames by which James's Jude, or Judas, was known generally in the Church." (Luke 6:16). [1]

The list below follows Matthew's list order:

Matt. 10:2-4	Mark 3:16-19	Luke 6:14-16	Acts 1:13, 26
Simon, who is called Peter	Simon (to whom he gave the name Peter)	Simon, whom he named Peter	Peter
Andrew, [Peter's] brother	Andrew	Andrew, [Peter's] brother	Andrew
James the son of Zebedee	James the son of Zebedee	James	James
John [James'] brother	John [James'] brother	John	John
Philip	Philip	Philip	Philip
Bartholomew	Bartholomew	Bartholomew	Bartholomew
Thomas	Thomas	Thomas	Thomas
Matthew the tax collector	Matthew	Matthew	Matthew
James the son of Alphaeus	James the son of Alphaeus	James the son of Alphaeus	James the son of Alphaeus
Thaddaeus	Thaddaeus	Judas the son of James	Judas the son of James
Simon the Zealot	Simon the Zealot	Simon who was called the Zealot	Simon the Zealot
Judas Iscariot	Judas Iscariot	Judas Iscariot	replaced by Matthias

So, there are no discrepancies.

Note

[1] Spence, H.D.M. Excel, Joseph. S. Pulpit Commentary, (Wm. B. Eerdmans, 1950), Luke 6:16 (https://biblehub.com/commentaries/luke/6-16.htm). Last Accessed 15 Nov. 2018.