Praying for the forgiveness of other believers???

1 John 5:16 "If anyone sees his brother committing a sin that does not lead to death, he will pray and ask and God will for him give life to those whose sin is not leading to death. There is a sin that leads to death; I do not say that one should pray for this."

❌I do not believe this is in relation to the Roman Catholic belief of praying for those in Purgatory.

✔ I do know that Priests could do a sacrifice for the community and Job did sacrifices for his children.

I was taught that outside of sacrifices, asking for foregiveness was only possible if a person asked with sincerity themself?

What are your thoughts on this?