Looking at [Paul's sins] from one angle his sin was the worst sin conceivable, but from another angle it is the sum of all sins because finally there is only one sin and that is the sin of unbelief.
That is the great New Testament doctrine on this matter; it is the thing that these people have to grasp above everything else, that we must not think in terms of particular sins but always in terms of our relationship to God. We all tend to go astray at the point. That is why we tend to think that some conversions are more remarkable than others. But they are not. It takes the same grace of God to save the most respectable person in the world as the most lawless person in the world. Nothing but the grace of God can save anybody, and it takes the same grace to save all. But we do not think like that. We think some conversions are more remarkable than others. Because we are wrong in our doctrine, we differentiate between sin and sin, and think some sins are worse than others. It all comes back to our relationship to God; it is all a matter of belief or unbelief.
From Martin Lloyd Jones' Spiritual Depression, page 71.