The Apostle Paul often referred to himself as the worst of sinners:
"To me, though I am the very least of all the saints, this grace was given..." ~ Ephesians 3:8
"For I am the least of the apostles, unworthy to be called an apostle, because I persecuted the church of God. But by the grace of God I am what I am, and his grace toward me was not in vain." ~ 1 Corinthians 15:9-10
"Christ Jesus came into the world to save sinners, of whom I am the foremost. But I received mercy for this reason, that in me, as the foremost..." ~ 1 Timothy 1:15-16
Does this mean that Paul was the worst sinner who ever lived? Obviously not. All people are equally sinful when stacked up against the Law of the Holy God of Scripture. What this means is that Paul understood himself to be the worst sinner that he knew. This is something that each of us truly can and should also say of ourselves, "I am the worst of sinners..." If we don't understand this then we won't understand grace.
We don't stop there, though. If we just left it there we would be the chief of the discouraged. Paul didn't leave it there. Even though Paul knew what a dreadful sinner he had been before Christ saved him and he also knew the current situation of his own heart, that he was still the worst of sinners (Romans 7:15-25), he never stopped being amazed at the grace that had been shown him in Christ. You can almost hear his awe and wonder, "To me this grace was given? I received mercy? The worst of sinners?" Paul was constantly reminding himself of the amazing grace of God in Jesus Christ. It was the natural response of a heart that understood that in light of his sin he was completely undeserving of such grace and mercy. Dwelling on these truths produced gratitude, contentment and glorious praise!
What about us? Are we (still) amazed that God has extended grace to sinners like us? Have we begun to grasp the depths of our sin? Have we begun to understand that God's grace is greater than all of our sins? Imagine what our lives would be like if we habitually first considered ourselves the worst of all sinners, then, after doing that, we went on and considered God's amazing grace extended to us in Jesus Christ. Imagine how having such thoughts of what our true nature is and what God has so wonderfully done for us would fuel our sanctification and our praise and worship of our thrice worthy God!
We should never forget God's amazing grace to sinners like us. It should be the first thought when we awake each morning and go to bed each night and all the thoughts in between. It was the considering of the mercy shown to him in Christ that would cause Paul to burst out in spontaneous words of praise:
Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways!