Albert Barnes Commentary 2 Peter 1:9

"For he that lacketh these things is blind, seeing only what is near, having forgotten the cleansing from his old sins." — 2 Peter 1:9 (ASV)

But he that lacks these things is blind. He has no clear views of the nature and the requirements of religion.

And cannot see afar off. The word used here (muwpazw), which does not occur elsewhere in the New Testament, means to shut the eyes; i.e., to contract the eyelids, to blink, to twinkle, as one who cannot see clearly, and hence to be near-sighted. The meaning here is that he is like one who has an indistinct vision; one who can see only the objects that are near him, but who has no correct apprehension of objects that are more remote. He sees only a little way into the true nature and design of the gospel; he does not take those large and clear views that would enable him to comprehend the whole system at a glance.

And has forgotten that he was cleansed from his old sins. He does not remember the obligation that grows out of the fact that a system has been devised to purify the heart, and that he has been so far brought under the power of that system as to have his sins forgiven. If he had any just view of that, he would see that he was under obligation to make as high attainments as possible and to cultivate to the utmost extent the Christian graces.