I don’t know where it comes from that people are always referring to sin but it didn’t come from the Bible. God is OMNI so He knows our past, present & future and He said we are forgiven. It doesn’t say ‘until’ or ‘if’ it says FORGIVEN.

He also said:
Rom 6:11
11 In the same way, count yourselves dead to sin but alive to God in Christ Jesus.
NIV

Now where people get that sin is still effecting any believer is not in the Bible because God said that we are free indeed:
John 8:36
36 So if the Son sets you free, you will be free indeed.
NIV

Sure there are some things that are not good to do but they have no effect on your salvation.

It’s there in print.