لَا يَمْلِكُونَ مِنْهُ خِطَابًا (...No one will have power to address Him,...78:37)
This sentence is probably connected to the preceding verse: جَزَاءً مِّن رَّبِّكَ عَطَاءً حِسَابًا (this being a reward from their Lord, a sufficing grant...78:36) In this case, it would mean that when Allah grants a certain grade of reward, no one dare speak about the grade as to why someone got more and others got less. But if this sentence is treated as an isolated one, it will mean that no one in the Plane of Gathering will have the power to speak to Him without His permission. This permission will be granted in some of the positions of Gathering, and not in others.