فـ : الفاء : واقعة في جواب شرط محذوف. تقديره وإذا علم أنه مسيء
the faa
here represents the phrase (which considered to be a response to another conditional phrase ,that doesn't exist but could be inferred from the meaning)
If he knows that he sinned..
I tried to translate the Iraab in English but don't think my translation is perfect,sorry If you can't understand me....