Tafsir of Ya seen 36:11

إنما تنذر من اتبع الذكر

You can only warn him who follows the Reminder, means, `only the believers will benefit from your warning, those who follow the Reminder,' which is the Qur'an.

وخشي الرحمن بالغيب

and fears the Most Gracious unseen. means, even when no one sees him except Allah, may He be blessed and exalted, he knows that Allah is watching him and sees what he does.

فبشره بمغفرة

Bear you to such one the glad tidings of forgiveness, (i.e., of his sins),

وأجر كريم

and a generous reward. means, one that is vast and great and beautiful. This is like the Ayah:

إن الذين يخشون ربهم بالغيب لهم مغفرة وأجر كبير

Verily, those who fear their Lord unseen, theirs will be forgiveness and a great reward. (67:12)