Block ANY access to wp-login.php and redirect to a given URL (here: home_url() ).

block-wp-login.php

<?php 

add_action( 'init', 'custom_init_function' );
function custom_init_function() {

	global $pagenow;

	if( ! is_user_logged_in() && 'wp-login.php' == $pagenow ) {
		wp_redirect( home_url() ); // redirect URL
		exit();	
	}	
}