"Therefore, if anyone is in Christ, he is a new creation; the old has gone, the new has come!" -- 2 Corinthians 5:17 (NIV)
This passage from the Apostle Paul's letter to the Church at Corinth tells us that when we accept Jesus' forgiveness and surrender to His lordship we become a new creation. One set of conditions or relationships has passed out of existence (absolutely); another set of conditions has come to stay (permanently, forever).
Just what has passed away? A worldview based on man's knowledge of the world. That would include a self-centered view of things. Moreover, what has come to stay? It is a cross centered view. The "cross of Jesus" changes all. Jesus paid the price of sin, our sin and everyone's own sin.
All who accept Christ's invitation to repent and receive forgiveness of the past behavior will become a new creation. We call this being "born again" as in John 3:16-17. We will see the world with new eyes. We will see from God's viewpoint. We will carry old memories, some old behaviors, but we will grow in the knowledge of God as we read the Bible and meditate on the Word. If we should slip and fall into old ways, there is a way of forgiveness and restoration. Read 1 John 1:9 below:
"If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness." -- 1 John 1:9 (NIV)
Many call this verse the "Christian's bar of soap."
Then you may want to read the whole paragraph of 2 Corinthians 5:16-21. Then meditating on what you read, you will see that while we are still in this world with its suffering and problems, we can live above that with renewed energy, a new view and a new purpose in this life.