It is clear that Paul expresses a very strong personal assurance of salvation and it is worth asking how he possessed such strong assurance. Here are some factors in the process of Paul's possession of assurance.
The first factor is from 1 Timothy 1:16, which tells us that Paul never forgot who he was by nature, a sinner: ‘The saying is trustworthy and deserving of full acceptance, that Christ Jesus came into the world to save sinners, of whom I am the foremost.’ Paul wrote these words after he had been a Christian for over three decades. We might imagine that a sense of sin would prevent a sense of assurance. But the opposite is the case. His awareness of his personal sinfulness caused Paul to retain an ongoing dependence on Jesus as his Saviour. It looks as if every time he sensed his sin Paul thought of Jesus.
The second factor comes from Galatians 6:14, which tells us that Paul understood what happened to Jesus on the cross. In that verse he exclaims, ‘But far be it from me to boast except in the cross of our Lord Jesus Christ, by which the world has been crucified to me, and I to the world.’ Paul knew that on the cross the penalty due by him for his sins was paid by Jesus.
The third factor comes from Romans 8:15, which informs us that Paul had an intimate prayer life with the Father. In that verse, Paul describes one of the privileges connected to the doctrine of adoption, intimate prayer in which we address God as Abba, Father. Although a sinner, Paul also knew that he was a child of God and therefore he had assurance.
The fourth factor is found in Romans 8:28 where Paul writes that ‘we know that for those who love God all things work together for good, for those who are called according to his purpose.’ Even when times were difficult, the apostle knew that somehow God could take him through it.
The fifth factor comes from Philippians 3:10, where Paul states the passion of his heart – to know Jesus more and more. This knowledge of Jesus was not merely intellectual although there is no doubt that Paul would have learned more about Jesus as time went on.
A sixth factor in Paul’s possession of assurance was his delight in thinking about the future world that Jesus will provide. He describes it from different perspectives: it is the restored creation, it is the state of final glorification, it is the presence of God, it is the possession of the inheritance, it is when God’s people are all together. But he thought about the future often and it gave him strong assurance.
The common detail in each of these factors in Paul’s assurance is the centrality of Jesus. We cannot have real assurance without dependence on, delight in, and devotion to Jesus. Therefore we need to imitate Paul in his pursuit of Jesus and when we do we will have assurance.