This is very similar to Load vim source files only if they exist. I use both of these in my vim configuration, which borrows from a lot of places. In some cases, much like this, it's difficult to tell for sure where this originated, but it's also simple enough it's OK to post.
" Function to source all .vim files in directory {
function! SourceDirectory(file)
for s:fpath in split(globpath(a:file, '*.vim'), '\n')
exe 'source' s:fpath
endfor
endfunction
" }
The above can be placed in ~/.vimrc or any place that's executed before code implementing it.
Here are some usage examples:
First, make a directory at ~/.vim/settings/ and make some .vim files there:
$ cd ~/.vim
$ mkdir settings
$ touch settings/
$ curl -o settings/sensible.vim https://raw.githubusercontent.com/tpope/vim-sensible/master/plugin/sensible.vim
tpope/vim-sensible is used in this example. I asked for permission to use it under a permissive license at tpope/vim-sensible#106.
Inside of ~/.vimrc, or anywhere after function! SourceDirectory(file):
call SourceDirectory('~/.vim/settings')
The SourceDirectory function, like SourceIfExists() keeps things DRY and things a bit more future proof when creating a modular config.