Show Content of Another Page

To show the content of another page, add this function:

function show_post( $path ) {
    $post    = get_page_by_path( $path );
    $content = apply_filters( 'the_content', $post->post_content );
    echo $content;
}

Then you can use that function where you want it:

show_post( 'about' );  // show content of page 'about'