(require 'org)

(defvar window-setup
  (setq org-agenda-window-setup 'only-window)
  (concat "Full-screen agenda."))

(use-package org
  :bind
  (("C-c a" . org-agenda)
   ("C-c c" . org-capture)
   ("C-c l" . org-store-link))
  :custom
  'window-setup)