What to use

[Ails]

What idioms to use if i would tell to a person that the last thing that i said should be the one that counts?

 

[Trisia]

What idioms to use if I would like to tell to a person that the last thing that I said should be the one that matters most?

[Not a teacher]

Well, there's "last but not least" -- but this means only that the last thing is at least as important as the others. It doesn't mean it's more important.

You could always say: "the last but most important thing is..."

Let's see, perhaps someone will come up with something very specific.

 

[David L.]

"Don't take any notice of what I said before."

"Forget what I said before."

"What I meant to say was.."

 

[Trisia]

Oh, I think I must have misunderstood the question then. *reddens*

If you mean that only the last thing you said is important, and the other things don't matter at all, by all means go with David L's suggestions.