“But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.”
2 Peter 1:9

He says add to your virtue, knowledge- this means study; give time to the diligent study of the word of God. The Bible says:
“Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.” 2 Timothy 2:15
At the end, he is the one that will give you the spirit of wisdom and revelation in the knowledge of him:
“That the God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him:” Ephesians 1:17
But you must prioritize and create time to study the word of God; as you increase in your knowledge of God, he says that your vision concerning the future and your state in Christ would be clear and not dark. There are Christians that by their actions, seem to show that they’ve forgotten that they’re not of this world and that Jesus has given them victory over every challenge, temptation, sin or habit, but he tells you the antidote to that forgetfulness is to abound in moral goodness, increase in your knowledge of God’s word, and spending time with the word of God would cause you to walk in temperance. Abounding in these would always remind you of your state as a Christian and the victory you have in Christ.