Form and Textcontent in Block
Try the following code

function commerce_bulk_invoice_block_view($block_name = '') {
  $block = array();
  if ($block_name == 'showinvoiceoptions') {
    $content = '&lt;div id="invoice-block"&gt;';
    if(!isset($_SESSION['selected_entities'])) {
        $content .= 'select a product first';
    } else {
        $content .= '&lt;h1&gt;SESSION Variables:&lt;/h1&gt;';
        foreach($entity_array as $book) {               
            $content .= '&lt;pre&gt;';
            $content .= print_r( $book, true );
            $content .= '&lt;/pre&gt;';
        }
    }

    $content .= '&lt;/div&gt;';  

    $build['content']=array('#markup' =&gt; $content);
    $build['form']=drupal_get_form('commerce_bulk_invoice_form');

    $block['content'] = $build;
 }
 return $block;
}