I might be wrong, so perhaps someone can clear this up - I always thought that “unto dust thou shalt return” referred to our bodies themselves turning to “dust”? That’s what “unto” means, right? “To”, as in, You are made of dust, and you’ll turn to dust again? Not that the body is returning to the dust of the earth?
Anyway, isn’t this to do with the resurrection of the body? We were supposed to just decompose at death and that’s the end, but because of Jesus’s sacrifice, our bodies aren’t going to disappear into dust at death forever but will rise again. That would be the point of burial or keeping the ashes together instead of throwing them away. Because we’re going to rise again, the body is also not destroyed or discarded as a symbol of this.
(Might also politely point out to your friend that no matter what they think those words “demonstrate”, we are to listen to the Church about this and honour what she teaches, not our own personal opinion. I’m always concerned when Catholics decide, “Well, the Church says this, but I think that…”)
