Because you have these blessings, you should try as much as you can to add these things to your life: to your faith add goodness; and to your goodness add knowledge;
If all these things are in you and they are growing, then these things will help you to never be useless. These things will help you to never be worthless in the knowledge of our Lord Jesus Christ.
But if a person does not have these things, then he cannot see clearly. That person is blind. He has forgotten that he was cleansed (forgiven) from his past sins.