2 Pt. 1:8-9

8 For if these qualities are yours and are increasing, they render you neither useless nor unfruitful in the true knowledge of our Lord Jesus Christ. 9 For he who lacks these qualities is blind or short-sighted, having forgotten his purification from his former sins.

Peter, in verse eight, implies that the seven qualities (in verses 5-7) should be continually increasing (of better and better quality); and each of them should increase in order to produce the growth of the following one, so that they all increase and grow together. For they are all connected to each other just as the parts of a tree are connected and grow together. But if one part, for some reason, is not growing, that will prevent the next part from growing. For example, if the young believer stops growing in knowledge (#2), that will affect his self-control (#3), and his perseverance, and his godliness, and the rest. Hence, each of the seven qualities need to increase and grow all together. The result will be that you will be useful to God in His kingdom and will bear much fruit.

But if one lacks these qualities (if he has not been diligent to produce them through his personal bible study and prayer and obedience to God) he is blind to his spiritual condition; that is, he will forget what Christ has done for him, and thus will lose his assurance of salvation. This is a sad situation—seeing a Christian become like a non-Christian, not even knowing for sure that he is saved.