Tafsir of Al-Qalam 68:49

Were it not that a favor from His Lord overtook him, which is the granting of success (tawfiq) to repent and the acceptance of it from him. It is read as "rahmah" (mercy instead of favor). The verb is masculine in both readings because the subject is a metaphorical feminine (ni'mah) separated by the pronoun. Abdullah [ibn Mas'ud] and Ibn Abbas read it as tadarakathu with the feminine 'ta'. Ibn Hurmuz, al-Hasan, and al-A'mash read it as tadarraka-hu with a shadda on the dal, the origin of which is tatadarraka-hu, where the 'ta' was changed into a 'dal' and the 'dal' was assimilated into the 'dal'. The intent is to narrate a past state, meaning: "Were it not that it would be said of him: tatadarakuhu (it overtakes him)."

He would have been cast forth into the wilderness (al-'ara'), meaning the land void of trees, that is, in this world. It is also said that it refers to the wilderness of the Resurrection, due to the Almighty's saying: Had he not been of those who glorify Allah, he would have remained in its belly until the Day they are resurrected. Its remoteness [from the intended meaning] is not hidden.

While he was blameworthy, this is in the position of a circumstantial qualifier (hal) for the subject of nubidha (cast forth). Upon it depends the answer to lawla (were it not), because the intention is the negation of his being cast forth in a state of blame; otherwise, the casting forth did occur. This indicates that his state was the opposite of blame, and the purpose is that the state of being cast forth and ending was contrary to the state of his beginning and initiation, based on the Almighty's saying: The fish swallowed him while he was blameworthy. In al-Irshad, it is stated that the conditional sentence is an initiation (isti'naf) introduced to clarify that the prohibited act was a matter to be cautioned against, resulting in dire consequences.