Tafsir of Ya seen 36:76

فﻼ يحزنك قولهم

So, let not their speech then grieve you. means, `their denying you and their disbelief in Allah.'

إنا نعلم ما يسرون وما يعلنون

Verily, We know what they conceal and what they reveal. means, `We know everything about them, and We will punish them for their false claims and deal with them accordingly on the Day when none of their deeds, great or small, major or minor, will be overlooked, and every deed they did throughout their worldly lives will be laid open for examination.'