On Psalm 51 - different perspectives on sin (words in italics are transliterated Hebrew, but without the accents)
The psalm begins (51.1-6) with a comprehensive analysis of the nature of sin as rebellion (pesa, transgression); as distortion (awon, iniquity); as failure (hattat, sin); as contrareity (against you, you only, have I sinned); as filth that needs to be cleansed (cleanse me... wash me); as falsehood and lack of authenticity and integrity (you desire truth [emet] in the inner parts) (p.137)
On 1 John 3.9; 5.18, that anyone born of God does not sin - here Ferguson offers a different view to that which I have been used to. Worth evaluating, I think.
Many commentators and versions understand John to be speaking here of sin as a prevailing habit. But the pointed language he uses (the Christian 'does not do sin') probably refers to the critical and radical deliverance from specific manifestations of the reign of sin which takes place at the point of union with Christ. Instead of remaining captive in concrete ways to the dominance of sin, the Christian becomes righteous precisely in those areas (cf. 1 Jn 2.29; 3.10). Thus the regenerate Saul seeks the fellowship, not the slaughter, of believers; the new man Zacchaeus gives money away rather than steals it; the transformed Philippian jailer cares for his prisoners rather than mistreats them; the runaway Onesimus, 'useless' in his old life, becomes a faithful servant and is 'useful' to Paul. (pp.129-130)