Was Paul serious when he said of himself, I am "the foremost of sinners" (1 Tim. 1:15), or was he just writing this for effect? "The foremost of sinners" is not how we usually think about Paul. To us he is a mighty gospel hero, the one who willingly went through off-the-charts suffering to extend the gospel, in fact the man to whom God actually revealed the heart and soul of the gospel and then commissioned him to preach it to the Gentiles.
No, Paul makes his perspective perfectly clear. God saved him to display "his perfect patience" towards sinners. He did this to encourage despairing sinners like you and me.
If we pause for a moment to reflect and meditate on Paul's past, his self-deprecating remarks make more sense. His friend, Luke, described what Paul was like before his conversion. He "ravaged the church" even "dragging off" men and women to prison (Acts 8:1-3). By self-admission Paul confessed to the sin of blasphemy (Ac 9:1-2), and remember, this was a serious sin. The penalty was death by stoning (Lev. 24:10-23). He was a "persecutor." He even labeled himself an "insolent opponent" of Christ's followers.
Much of Paul's self-loathing flowed out of his Judaism. Although he he was born under the law, and committed to it, he was unfaithful to it. In Romans two he condemns himself with his own words. He knew the law but did not keep it. Therefore, he was worse than the Gentiles who had no knowledge of God's law. Apart from Christ he knew he faced a severe judgment.
In addition, he was a Pharisee. As such he was puffed up in religious pride. In Phil. 3:2 he described Pharisees like himself as "dogs, evildoers, those who mutilate the flesh." Paul knew that in God's sight, and apart from grace, he was a "dog" an "evildoer."In fact, his propensity to pride and boasting was so great that, even after his conversion, God was forced to give him a "thorn in the flesh...a messenger of Satan" to harass him (2 Cor. 12:8).
Paul was actually a blessed man, and he knew it. He was most blessed because God had given him a clear view of himself. He possessed the self knowledge that many of us today lack. In fact, his clear understanding of who he was apart from God's grace, rather than a negative, actually proved the depth of his relationship with God. For the more one knows God the less he thinks of himself, and the more he thinks of God.
There is an old saying that sums up Paul and his life. To the degree that sin becomes bitter grace becomes sweet. God made Paul's sin "bitter" in his own sight. Therefore, Paul served God extravagantly. He knew that of which he had been forgiven. In the words of Jesus, "He that is forgiven little loves little" (Luke 7:47). His great sufferings, chronicled in 2 Cor 11:21-29 point to the knowledge of a great love proceeding from the knowledge of great sin forgiven.
Is that how we see it? Is that how the spiritual life works for you me? Most of us think that the closer we get to God the more satisfied we will become with our spiritual progress, the more contented we will be with our spiritual victories, and the less we will think about our sin.
The truth is just the opposite.
The closer we get to God the clearer we see the bright whiteness of his holy moral purity, and the more we see our own imperfections by contrast. Before we thought little of lying. Now a simple exaggeration alarms us. The closer we get to God the more amazed we become that he chose us, that he would send his Son to bear the wrath that we so justly deserve. In other words, as we get closer to God we become more satisfied with God and less satisfied with our self. We trust God more and trust self less. We need God more and need self less. We are more dissatisfied with our spiritual progress and more satisfied with all that God has done and become for us.
This was Paul's experience. It is why with great conviction he could describe himself as the "foremost" of sinners. In fact, this been the increasing conviction of all of God's servants. To the degree that sin becomes bitter grace becomes sweet.
Listen to Jonathan Edwards. “Such is the nature of grace, and of true spiritual light, that they naturally dispose the saints in the present state, to look upon their grace and goodness little, and their deformity great. And they that have the most grace and spiritual light, of any in this world, have most of this disposition.” 
Because God was kind to Paul, he saw himself as the chief of sinners. How about you and me? When you are tempted to give up because of that repeated sin that has again just reared its ugly head, do you remember God's grace to Paul, the foremost of sinners. When you become discouraged and wonder if you will get the grace you need to persevere to the end, remember God's grace to Paul, the foremost of sinners.
Paul was the poster boy for "unmerited favor," the kind that comes to every person that believes the gospel everyday.
Soli Deo Gloria!