on the day yawma is the adverbial qualifier for lā yamlikūna ‘they will not be able to’ when the Spirit Gabriel or God’s hosts and the angels stand arrayed saffan is a circumstantial qualifier in other words mustaffīna. They creatures will not speak except him whom the Compassionate One permits to speak and who says what is right from among the believers and the angels as if meaning that they will intercede for he whom He approves of.