Your question is a little confusing, but I suspect you actually mean that you've byte-compiled the
prelude-ivy.el library (as opposed to "reading the source file"), and that the compiler has produced a warning that the function
prelude-require-packages is not known to be defined (n.b. not "prelude-required-packages", which does not appear anywhere in the file; and the warning would be quite specific about it being a function, rather than a "symbol", which is not known to be defined).
The warning would look like this:
In end of data:
prelude-ivy.el:71:1:Warning: the function ‘prelude-require-packages’ is not
known to be defined.
(And for future reference, if you have a question about a warning or error message, you should always copy and paste that message into your question -- doing so here would have eliminated all the confusion.)
The message tells us that the byte-compiler got all the way through the file and never encountered a definition for that function, even though it was used earlier in the file:
(prelude-require-packages '(ivy swiper counsel))
The warning (which will indeed be harmless in practice) can be silenced by informing the byte-compiler where the function
prelude-require-packages is defined:
(declare-function 'prelude-require-packages "prelude-packages")