"Then We shall surely relate to them," meaning their deeds, "with knowledge" of them, "and We were not absent" from their deeds.
﴿فلنقصن عَلَيْهِم﴾ أَي: أَعْمَالهم ﴿بِعلم﴾ بهَا ﴿وَمَا كُنَّا غائبين﴾ عَن أَعْمَالهم.