Matthew Poole and continuators on 2 Peter 1:9

9 But he that lacketh these things , is blind , and cannot see afar off , and hath forgotten that he was purged from his old sins .

He that doth not live in the Exercise of the fore-mentioned Graces.

Spiritually blind, as being destitute of saving Knowledge.

The Greek word is variously translated; the most probable account of it is either, 1. that it signifies to feel the way, or grope as blind Men do; and then the meaning is, He that lacketh these things in blind, and as a blind Man, gropes, not knowing which way to go; he is really destitute of the Knowledge he pretends to: Or, 2ly, to be pore-blind, or short-sighted, so as to see things near hand, but not afar off, as our Translation hath it; and then the sense is, That such a one sees only the things of the World, but cannot look so far as Heaven to discern things there, which if he did, he would walk in the way that leads thither, viz. in the Practice of the Duties before prescribed.

He is judged in the sight of God, to forget a Benefit received, that is not effectually mindful of it, in living sutably to it. And so here, he that professeth himself to have been purged from his old Sins, in Justification and Santification, by the Blood and Spirit of Christ, 1 Cor. 6.11. Ephes. 5.25, 26, 27. and yet still lives in Sin, and in the neglect of the Duty he is engaged to, practically declares his Forgetfulness of the Mercy he professeth to have been vouchasafed him; and accordingly may be interpreted, to have forgotten it, in that he acts like one that had. Or, if this be understood of one that is really purged from his old Sins, yet he may be said to forget that so far as he returns again to them, or lives not up to the ends of his Purgation, Luke 1.74, 75.

Marginal references: 1 Joh. 2.9, 11.