قُلِ ٱللَّهُ أَعْلَمُ بِمَا لَبِثُوا۟ ۖ لَهُۥ غَيْبُ ٱلسَّمَـٰوَٰتِ وَٱلْأَرْضِ ۖ أَبْصِرْ بِهِۦ وَأَسْمِعْ ۚ مَا لَهُم مِّن دُونِهِۦ مِن وَلِىٍّ وَلَا يُشْرِكُ فِى حُكْمِهِۦٓ أَحَدًا Qur’an Al-Kahf (18:26)Quli Allahu aAAlamu bima labithoo lahu ghaybu alssamawati waalardi absir bihi waasmiAA ma lahum min doonihi min waliyyin wala yushriku fee hukmihi ahadan
Who are "they" in this sentence? They may be the Companions of the Cave, for they put themselves under the protection of Allah, and disowned all attribution of partners to Him. Or "they" may refer to the people in general who go wrong and become "Mushriks" i.e., attribute imaginary partners to Allah.
His Command: i.e., Allah's sovereignty of the world, or in His Judgment on the Day of Judgment.