If I understand it correctly, you have one parent page "Writing" and on that you'd like to list all of your writings which are subpages.
To do that, you first need to create a page template which is separate from the default template every other page uses.
It's as easy as simply making a copy of page.php and calling it page_writings.php.
Now you need to first remove the line of code you added above from the page.php, but leave it in your new page_writings.php.
Then you need to tell WordPress that your newly created page_writings.php is actually a page template - you do that by editing it and before anything else, first thing on the page, you paste this code:
Template Name: Writings
Save the file and upload it to the same folder as all your other theme's files, along with the also edited page.php (without the line of code above).
The only thing left to do now is tell WordPress to use your new template for the specific pages you want the subpage listing to appear on: In your Admin area, go to "edit page" and way down, under the editor box, there is a box called "Page Template". If you did all of the above right, your new page template "Writings" should appear there - select it, save, and you're done.
If you want that subpage listing to appear on your subpages as well, you must go into each one and select this template for them as well.
Hope this helps!