post-grid-loop.php

<?php
function my_post_grid() {

	global $wp_query;
	global $post;

	// Open first row
	echo '<div class="row">';

	$i = 1;
	while ( have_posts() ) {
		the_post();
		$thumb = wp_get_attachment_image_src( get_post_thumbnail_id(), 'full' ); // We want the URL to the full size image
		?>
		<div class="col-sm-3">
		    <div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
			<h2 class="entry-title"><?php the_title(); ?></h2>
			<a href="<?php echo $thumb[0]; ?>" class="themeblvd-lightbox mfp-image">
				<?php the_post_thumbnail('grid_3'); ?>
			</a>
			<?php the_content(); ?>
		    </div>
		</div>
		<?php
		// Every 4th post, but not the very last post
		if ( $i % 4 == 0 && $i != $wp_query->post_count ) {

			// Close current row
			echo '</div><!-- .row (end) -->';

			// Open next row
			echo '<div class="row">';

		}

		// Increment the counter
		$i++;
	}

	// End final row
	echo '</div><!-- .row (end) -->';
}