2 Corinthians 5:17
Something fundamentally changes when you accept Christ. Something profound and New takes place, that cannot have any part with the old (2 Corinthians 6:14).
Now for many, this is unrealized in this life, unless they are taught. A Christian might live their whole life, and never realize what all Christ has bought for them. But, as Jesus said, when a man believes, he is born again of a spiritual seed (John 3:3-5), and the old things are “passed away”.