This means that when you hear two voices at the same time, you have to choose which one you will focus on.
لِذٰلِكَ ،‏ حِينَ يُكَلِّمُكَ شَخْصَانِ فِي ٱلْوَقْتِ نَفْسِهِ ،‏ عَلَيْكَ أَنْ تَخْتَارَ ٱلِٱسْتِمَاعَ إِلَى أَحَدِهِمَا .‏