Changing font in my Vim text editor on Arch Linux? (DWM/X11)

I need your help! I am trying to set up a specific font and font size in my

~/.vimrc

file using

guifont=Monospace:h15

, but nothing is changing no matter if I put 12 or 20 in the size column. I've tried several fonts also, but it seems like changes just not apply - after writing the file and reopening it, size of the font and the font itself stays the same. Also

:set guifont=*

command doesn't show me anything. Here is my

.vimrc

file:

set nocompatible
filetype off

set rtp+=~/.vim/bundle/Vundle.vim
call vundle#begin()

Plugin 'VundleVim/Vundle.vim'
Plugin 'nyngwang/nvimgelion'

syntax on

set termguicolors

set guifont=Monospace:h20

call vundle#end()
filetype plugin indent on

au BufNewFile, BufRead *.py
	\ set tabstop=4
	\ set softtabstop=4
	\ set shiftwidth=4
	\ set expandtab
	\ set autoindent
	\ set fileformat=unix

set laststatus=2

set wrap

set encoding=utf-8

vnoremap  :w !xclip -i -sel c

How to set up a specific font in my Vim configuration file? Thank you for your help.