>all Christians should believe

I think this is the point being made: your 'should', and by extension your quote, has no meaning when grace is defined as the single goal of spiritual life, and then is reduced to a simple transaction.

Sure, people are free to believe whatever. I am quoting the very scripture they claim to believe though and so it would be hypocritical to do otherwise

The term we have for those folks is that they're doing "easy-believism" and it's broadly a pitfall within Christianity. It's not considered normative to so heavily lean on grace in the way that you're describing