As with the English expression 'From A to Z' (which is similar to what 'first and last' is paired with in Revelation, i.e., 'I am Alpha and Omega'), it is a vague phrase.
In Isaiah, it is related to time and in particular first generation to last (41:4), being the only real God (44:6), and God's relationship with Israel (48:12).
It is an incomplete phrase in ...
"First and Last" as title of Jehovah occurs three times in Isaiah.
“Who has performed and accomplished it, Summoning the generations from
the beginning? ‘I, the LORD, am the first, and with the last. I am
Gill summarizes the intended meaning here about Jehovah's eternal unchanging nature as the idiom of "generations" ...