From A.J Krailsheimer's Conversion (1980) - AJK was the English translator of Pascal's Pensees for the Penguin edition. He was a scholar at Christ Church, Oxford.
Implicit in the idea of conversion is that of forsaking the past unconditionally and accepting in its place a future of which the one certain fact is that it will never allow the previous pattern of life to be the same again...
One result of conversion seems always to be that the past, however apparently blameless before, begins to be revalued, even rewritten.
The convert will see his newly found identity and response to Christ as real; all that previously kept him from it as shadowy, false, or empty.
The sense of guilt is a natural enough concomitant of a conventionally sinful life, but the sense of emptiness, 'vanity' in scriptural terms, is more fundamental.
As the new relationship with Christ develops, the earlier time spent without it appears more and more of a waste.