Add in a base render.php.

src/blocks/call-to-action/render.php

@@ -0,0 +1,34 @@
+<?php
+/**
+ * Displays the Call to Action block.
+ *
+ * @package WDS_Gutenberg
+ * @since NEXT
+ */
+
+namespace WDS_Gutenberg\Src\Call_To_Action;
+
+/**
+ * Render block: Related Posts.
+ *
+ * @param array $attributes The attributes passed in from the Related Post block settings.
+ * @return string The block markup.
+ *
+ * @since NEXT
+ */
+function render_block( $attributes ) {
+
+	ob_start(); ?>
+
+	<!-- wp:wds/related-posts -->
+	<?php \WDS_Gutenberg\Src\Block_Options\display_block_options( $attributes ); ?>
+
+		<?php \WDS_Gutenberg\Src\Component\display_block_title( $attributes ); ?>
+
+	</section>
+	<!-- /wp:wds/related-posts -->
+	<?php
+
+	return ob_get_clean();
+}
+register_block_type( 'wds/call-to-action', [ 'render_callback' => __NAMESPACE__ . '\\render_block' ] );