Paul was an apostle who was “untimely born” (1 Corinthians 15:8). This means that he did not meet the only stated New Testament qualification for an apostle: One who has “accompanied us all the time that the Lord Jesus went in and out among us—beginning with the baptism of John until the day that He was taken up from us— one of these must become a witness with us of His resurrection" (Acts 1:21-22).
The eleven disciples apparently had picked up along the way with Jesus this idea that a “witness to the resurrection” should have been there all along the way.
Paul was not.
Why did God choose Paul and thus make such an exception to the will of the eleven apostles gathered in the upper room?
Perhaps the answer is found in 1 Timothy 1 where Paul gives the briefest of biographies (something a number of testifiers could learn from). He says he was a blasphemer and a persecutor.
Yet he found mercy so “Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life” (1 Timothy 1:16).
In other words, Paul’s salvation and subsequent ministry is a reminder to us all that God is not limited by our past, and Jesus is bigger than our past.
It is a reminder to us who have sinned (and who among us hasn’t).
It is also a reminder to us about those to whom God has called us to minister.
Let us not forget that if God saved Paul and used him to turn the world upside with the gospel, whoever you are working with is not beyond the reach of that kind of mercy.