Tafsir of Az-Zumar 39:56

أن تقول نفس يا حسرتى على ما فرطت في جنب الله

Lest a person should say: "Alas, my grief that I was undutiful to Allah...'' means, on the Day of Resurrection, the sinner who neglected to repent and turn back to Allah will regret it, and will wish that he had been one of the righteous who obeyed Allah.

وإن كنت لمن الساخرين

and I was indeed among those who mocked. means, `my actions in this world were those of one who ridicules and makes fun, not of one who has firm faith and is sincere.'

أو تقول لو أن الله هداني لكنت من المتقين