Tafsir of Al-Mujadilah 58:18

(The Day God will resurrect them all) — The discussion regarding its counterpart has preceded recently.

(Then they will swear to Him)—meaning to God Almighty on that day—saying: (By God, our Lord, we were not polytheists.) Just as they swear to you in this world that they are Muslims like you. The comparison is based solely on the act of swearing in this world, even if the object of the oath differs, based on what we have previously established regarding the occasion of the revelation.

(And they think)—in the Hereafter—(that they are upon something)—meaning, by those wicked oaths—regarding the bringing of benefit or the warding off of harm, just as they were in this world, where they used them to protect their lives and properties and to acquire worldly benefits.

(Indeed, it is they who are the liars) — those who have reached the ultimate limit of lying, for which there is no further limit, as they have dared to lie before the Knower of the Unseen, imagining that their wicked oaths would make falsehood acceptable to Him, Majestic and Exalted, just as they make it acceptable to the believers.