The phrase 'Last but Not Least' is used to denote that something you say is last in sequence but not least in importance.
Example of Use: “Last but not least, I’d like to introduce my grandmother, Rosie.”
The idea, if not the phrase 'last but not least,' may originate in the Bible, where in John Wyclif’s 1382 version of Matthew, 19:30, the statement “the firste the laste, and the laste the firste” can be found.