"And those whom they call upon besides Him do not possess," meaning the idols do not possess the power to intercede for their worshipper. "Except those who testified to the truth," He says: Intercession is only for those who testified to the truth in the worldly life, "while they know" that it is the truth; the angels shall intercede for them.
﴿وَلَا يَمْلِكُ الَّذِينَ يَدْعُونَ مِن دُونِهِ﴾ يَعْنِي: الْأَوْثَان لَا تملك أَن تشفع لعابدها ﴿إِلَا مَن شَهِدَ بِالْحَقِّ﴾ يَقُول: إِنَّمَا الشَّفَاعَة لمن شهد بِالْحَقِّ فِي الدُّنْيَا ﴿وَهُمْ يَعْلَمُونَ﴾ أَنه الْحق؛ تشفع لَهُم الْمَلَائِكَة.