The word ﴾ثُمَّ﴿ “Then” is a conjunction which shows ‘a delay in time until the subsequent happening’. On the other hand, the conjunction Fa’ shows ‘an immediate subsequent happening’.
Thus, the usage of the word ﴾ثُمَّ﴿ “Then” means that the speech is now moved to address the Jews who were in Medina during the revelation period of the Holy Qur’an. They were of two groups, a group who were allies with the tribe of Aws and a group who were allies with the tribe of Khazraj. Therefore, when a battle broke out between the Aws and Khazraj, one group of Jews would fight together with the Aws and the other would fight with the Khazraj. Thus, one group of Jews would end up killing the other and evicting them from their homes.
﴾تَظَاهَرُونَ عَلَيْهِمْ﴿“cooperating against them”: That is, You help a group to overcome another.
﴾ِبِالإِثْمِ وَالْعُدْوَان﴿ “in sin and aggression”: The word Ithm means ‘aggression without the right to do so’ and the word ‘Udwan means ‘the exceeding of the limits’.
The meaning of these parts of the verse is that after these battles, there will be the ransoming of the captives. The plural form of the word Asiir which means a captive, is normally the word Asraa, as we can find in the following:
﴾مَا كَانَ لِنَبِيٍّ أَنْ يَكُونَ لَهُ أَسْرَى حَتَّى يُثْخِنَ فِي الأَرْضِ﴿
“It is not fitting for a prophet that he should have prisoners of war until he has thoroughly subdued the land” [Surah Al-Anfaal: 67].