Why did God extend mercy and grace to Paul first?
God extended mercy and grace to Paul first because Paul was the chief of sinners and at the head of the line. Since Paul would serve as Apostle of the Gentiles, God showed longsuffering in him as a pattern for all who would afterward believe on Jesus Christ and receive everlasting life.
Les explains that Paul was the chief of sinners, not the worst, but at the head of the line. Because Paul was to play the role of the Apostle of the Gentiles, God extended mercy and grace to him first, so that in him God might show forth longsuffering as a pattern that everything else would fall into. That pattern was for those who would hereafter believe on Jesus Christ and by believing have life everlasting. Les also notes Paul’s constant defense of his apostleship, that he was the one who brought the Gospel to the Gentiles, and that he is the only one who claims to have had the mysteries revealed to him. In 1 Corinthians 3, Paul refers to the grace of God given unto him as a wise master builder.