Which function should be used to load a package in R, require or library?

The main difference between require and library is that require was designed to use inside functions and library is used to load packages. If a package is not available then library throws an error on the other hand require gives a warning message.

Using library

> library(xyz)
Error in library(xyz) : there is no package called ‘xyz’

Using require

require(xyz)
Loading required package: xyz
Warning message:
In library(package, lib.loc = lib.loc, character.only = TRUE, logical.return = TRUE, :
there is no package called ‘xyz’

Here we can see that the library shows an error and require gives a warning message, since warnings are mostly avoided and we tend to move further hence require is not recommended because further steps will throw an error or warning again.