﴿ ثُمَّ ءَاتَيْنَا مُوسَى ٱلْكِتَٰبَ تَمَامًا عَلَى ٱلَّذِىٓ أَحْسَنَ وَتَفْصِيلًۭا لِّكُلِّ شَىْءٍۢ وَهُدًۭى وَرَحْمَةًۭ لَّعَلَّهُم بِلِقَآءِ رَبِّهِمْ يُؤْمِنُونَ ﴾

“AND ONCE AGAIN: We vouchsafed the divine writ unto Moses in fulfilment [of Our favour] upon those who persevered in doing good, clearly spelling out everything, and [thus providing] guidance and grace, so that they might have faith in the [final] meeting with their Sustainer.”

Then thumma is for describing events in a sequence We gave Moses the Scripture the Torah complete in grace for him who does good by observing it and a detailing an explanation of all things needed for religion and as a guidance and a mercy that perhaps they that is the Children of Israel might believe in the encounter with their Lord through the Resurrection.