When we become a Christian, we are literally spiritually joined to God through our union with Christ. The very life and nature of God comes to live on the inside of us by the indwelling presence of the Holy Spirit.
We become partakers of the divine nature of God. Our very spiritual DNA is changed from sinner to saint, from lost to saved, from darkness to light, and from unrighteousness to righteousness.
God takes out of us the corrupt nature of sin and recreates our spirit with His life and nature.
We are not merely forgiven sinners. The nature of the sinner is sin, while the nature of the believer is righteousness. The sinner sins because that is their nature, but the Christian’s nature is contrary to sin. While he/she may commit sins, this is in direct opposition to the nature of Christ residing in their spirit.
It is unscriptural to declare that we are sinners saved by grace. We were sinners, we were saved by grace, and now we are the righteousness of God in Christ Jesus. 2 Corinthians 5:21, Romans 8
2 Corinthians 5:17 (NKJV) Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.