Our first introduction to Saul (later called Paul) in Acts.

Acts 8:1 Saul approved of Stephens death (by public stoning)
He was not actively throwing stones, but was helping those who did.

Acts 8:3 Saul began to destroy the church
He moved on from being just a helper to active involvement.

Acts 9:1 Saul breathing out murderous threats sets off for Damascus
He appears to have impressed the key leaders of the persecution.

Acts 15:39 Saul and Barnabus had such a sharp disagreement ...
In light of Saul's history are you glad not to have been in the room?
Barnabus (means Son of Encouragement) was the nickname the church gave a guy called Joseph (Acts 4:36).
No nickname recorded for Saul - the church was afraid of him and would not accept him (Acts 9:26).
In Latin the name Paul means "small" or "humble" - appropriate for his later ministry (see 1 Corinthians 2:1-5).

Paul's testimony about himself

1 Timothy 1:13-17 ... blasphemer ... violent ... worst of sinners ...
Outdone only by the grace, mercy and endless patience of Christ Jesus (see 2 Peter 3:9).

Examples of Paul's Teaching

Colossians 3:11-13 Bear with each other, forgive whatever grievances you may have ...
Was Paul reminded of his history with Barnabus, Mark, and maybe others when he wrote that?
Was he preaching to himself?

Philipians 4:6 Do not be anxious about anything ...
In Acts 16:6-8 we read that Paul and his companions were frustrated in their endeavours to preach in certain places. Luke records that they were restrained by the Holy Spirit and the Spirit. Is Luke using the wisdom of hindsight as he recorded the events of those days. What was the practical outworking of this restraint - visas, tickets, money, people not keeping promises, ... was Paul getting anxious, angry, mad ...? Did something similar occur in Acts 27:9-11, 21 and Paul had to restrain his anger at the decision of others (see Romans 8:21-25).

Acts 16:25 About midnight Paul and Silas were praying and singing hymns
Having, some hours earlier, been wrongly arrested and experienced 'beat up first, ask questions later' police brutality that's some 'sacrifice of praise' (Hebrews 13:15). I wonder what was going on in the meantime, the conversations he and Silas had. They lived what Peter taught when he wrote 'Humble yourselves ... cast all your anxiety on him ... be self-controlled and alert' (1 Peter 5:6-9). Paul wrote similar to the church in Philipi, the same place where the Acts 16 incident took place (Philipians 4:4-6), guys who had seen him live it out (see 1 Corinthians 11:1, Philipans 3:17).