I was having a discussion with someone who believes that when you are born again, God only forgives you for your past sins before you were born again and not your future sins. Is there a scripture that says or implies specifically that Jesus died for our future sins after being born again?
There are several.
In Colossians 2:13 Paul wrote, “He forgave us all our sins”. The Greek word translated “all” means each and every, any and all. That means when we are born again all our past, present, and future sins are forgiven.
In Ephesians 1:13-14 he said our salvation was guaranteed from the time we believed. How could he have said that unless our future sins had been forgiven as well as our past ones? He said essentially the same thing in 2 Cor. 1:21-22, 2 Cor. 5:5 and Ephesians 4:30.
In Hebrews 10:14 the writer said, “Because by one sacrifice He has made perfect forever those who are being made holy.” How could God see us as perfect forever unless all our sins had been forgiven?
Had this not been the case, everyone who has been saved would have to remain absolutely sin free for the rest of his or her life. That means we would become responsible for keeping ourselves saved. This is a violation of Ephesians 2:8-9 which says we’re saved by grace and not by works, lest anyone should boast. Certainly those who were able to remain sin free for the rest of their lives would have something to boast about.
The fact is, remaining sin free is humanly impossible by God’s standards, because to do so we would have to be perfect, as our Heavenly Father is perfect (Matt. 5:48). Since we can’t be as perfect as God is, we would all have been lost again within a short time, and the Lord’s death would have amounted to nothing.
To prevent this, God imputed to us a righteous equal to His own. We can’t earn this righteousness by trying to be perfect. It comes through faith in Jesus Christ to all who believe. For all have sinned and fall short of the glory of God and are justified freely by His grace through the redemption that came by Christ Jesus (Romans 3:21-24). He is able to save completely those who come to God through him, because he is at the right hand of God and is always interceding for us (Romans 8:33-34, Hebr. 7:25).