John Mark

Who was "John called Mark" (Acts 15:37)?
John Mark was the son of Mary to whose house Peter went after the angel freed him from the prison in Jerusalem: "So, when he had considered this, he came to the house of Mary, the mother of John whose surname was Mark, where many were gathered together praying" (Acts 12:12). Paul and Barnabas brought John Mark with them when they returned to Antioch of Syria after delivering the relief for the brethren suffering in Jerusalem during the Great Famine: "And Barnabas and Saul returned from Jerusalem when they had fulfilled their ministry, and they also took with them John whose surname was Mark" (Acts 12:25).

Why didn't Paul want to take John Mark along on their second journey?
John Mark had deserted them in Perga of Pamphylia during their first missionary journey: "Now when Paul and his party set sail from Paphos, they came to Perga in Pamphylia; and John, departing from them, returned to Jerusalem" (Acts 13:13). So "Paul insisted that they should not take with them the one who had departed from them in Pamphylia, and had not gone with them to the work" (Acts 15:38).

Then why was Barnabas determined to take John Mark with them?
While the reason isn't stated, there are at least two possibilities. For one, John Mark was his cousin: "Mark the cousin of Barnabas" (Colossians 4:10). For another, Barnabas, whose name means "Son of Encouragement" (Acts 4:36), was a 'people person' who was inclined to encourage and include others. After all, when the disciples in Jerusalem were "afraid" (Acts 9:26) of Saul the persecutor of Christian when he returned to Jerusalem as a Christian, it was Barnabas who met with Paul and "brought him to the apostles" (Acts 9:27).

Between Paul and Barnabas, who was right about taking or not taking John Mark?
Barnabas prioritized John Mark being given a second chance, while Paul prioritized having a reliable partner for the rigors of missionary work. Both of them were sincere and had valid points.

Was Satan again trying to create dissension?
Perhaps

If so, did he succeed?
Yes, in two teams of missionaries being sent out instead of just one to strengthen the body of Christ, who wins again: "And so Barnabas took Mark and sailed to Cyprus; but Paul chose Silas and departed, being commended by the brethren to the grace of God. And he went through Syria and Cilicia, strengthening the churches" (Acts 15:39-41).* Moreover, Paul's later comments indicate that John Mark eventually grew into someone very reliable: "Aristarchus my fellow prisoner greets you, with Mark the cousin of Barnabas (about whom you received instructions: if he comes to you welcome him), and Jesus who is called Justus. These are my only fellow workers for the kingdom of God who are of the circumcision; they have proved to be a comfort to me" (Colossians 4:10-11).

What brought about John Mark's growth?
Perhaps personal coaching and encouragements from Barnabas, the "Son of Encouragement" during their missionary journey together.

Which type of people does God use to expand His kingdom: goal-oriented people like Paul or people-oriented people like Barnabas?
Both: "There are diversities of gifts, but the same Spirit. There are differences of ministries, but the same Lord. And there are diversities of activities, but it is the same God who works all in all" (1 Corinthians 12:4-6).