"And this secure city." It means: the safe place, referring to Mecca. He says: You are safe within it from killing and enslavement, while the Arabs would kill one another and enslave one another, and this was before the command to fight.
﴿وَهَذَا الْبَلَد الْأمين﴾ يَعْنِي: الْآمِنَ يُرِيدُ مَكَّةَ؛ يَقُولُ: إِنَّكُمْ تَأْمَنُونَ فِيهِ مِنَ الْقَتْلِ والسِّبَاءِ، وَالْعَرَبُ تَقْتُلُ بَعْضُهَا بَعْضًا، وَتَسْبِي بَعْضُهَا بَعْضًا، وَكَانَ هَذَا قبل أَن يُؤمر بِالْقِتَالِ
