ثُمَّ يَتُوبُ ٱللَّهُ مِنۢ بَعْدِ ذَٰلِكَ عَلَىٰ مَن يَشَآءُ ۗ وَٱللَّهُ غَفُورٌ رَّحِيمٌ
Summa yatoobul laahu mim ba'di zaalika 'alaa mai yashaaa'; wallaahu Ghafoorur Raheem
Then, after that, God turns in mercy to whomever he wills. God is forgiving, merciful.
Every verb around this one is finished: God helped, sent down forces, punished. The turning here stands in the unfinished tense, and it is offered to the same side that the previous line leaves under punishment. God's willing is the only condition named, which puts the door outside anyone's power to close.