Код галереи, созданный в модуле Pinegrow Blocks WP (lesson 10).

gallery_pgwp_blocks.php

<section class="content-block gallery-1 gallery-1-1">
    <?php
        $gallery = blocks_get_gallery( get_theme_mod( 'blocks_gallery_1_1_source' ) );
    ?>
    <div class="container">
        <div class="underlined-title">
            <h1><?php echo get_theme_mod( 'blocks_gallery_1_1_title', __( 'A selection of our work', 'blockswpdemo' ) ); ?></h1>
            <hr>
            <h2><?php echo get_theme_mod( 'blocks_gallery_1_1_subtitle', __( 'Hand-picked just for you', 'blockswpdemo' ) ); ?></h2>
        </div>
        <ul class="filter">
            <li class="active">
                <a href="#" data-filter="*">
                    <?php _e( 'All', 'blockswpdemo' ); ?>
                </a>
            </li>
            <?php foreach($gallery['tags'] as $tag_slug => $tag_name) : ?>
            <li>
                <a href="#" data-filter="<?php echo '.'.$tag_slug ?>">
                    <?php echo $tag_name ?>
                </a>
            </li>
            <?php endforeach; ?>
        </ul>
        <!-- /.gallery-filter -->
        <div class="row">
            <div class="isotope-gallery-container">
                <?php foreach($gallery['images'] as $image) : ?>
                <div class="col-md-3 col-sm-6 col-xs-12 gallery-item-wrapper <?php echo $image['tags_string'] ?>">
                    <?php
                        //Press CMD+H to edit. Your PHP code comes here...
                    ?>
                    <div class="gallery-item">
                        <div class="gallery-thumb">
                            <img src="<?php echo $image['thumbnail'][0] ?>" class="img-responsive" alt="<?php echo $image['thumbnail']['alt'] ?>">
                            <div class="image-overlay"></div>
                            <a href="<?php echo $image['image'][0] ?>" class="gallery-zoom" alt="<?php echo $image['alt'] ?>"><i class="fa fa-eye" alt="This is the title"></i></a>
                            <a href="<?php echo $image['link'] ?>" class="gallery-link" target="_blank"><i class="fa fa-link"></i></a>
                        </div>
                        <div class="gallery-details">
                            <h5><?php echo $image['title'] ?></h5>
                        </div>
                    </div>
                </div>
                <?php endforeach; ?>
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
                <!-- /.gallery-item-wrapper -->
            </div>
            <!-- /.isotope-gallery-container -->
        </div>
        <!-- /.row -->
    </div>
    <!-- /.container -->
</section>

<!-- Functions.php section Customizer Controls -->

    $wp_customize->add_section( 'blocks_gallery_1_1', array(
        'title' => __( 'Галерея', 'blockswpdemo' )
    ));

    $wp_customize->add_setting( 'blocks_gallery_1_1_source', array(
        'type' => 'theme_mod'
    ));

    $wp_customize->add_control( new WP_BlocksContentDropdown_Customize_Control( $wp_customize, 'blocks_gallery_1_1_source', array(
        'label' => 'Источник контента (пост с галлереей)',
        'type' => 'custom',
        'section' => 'blocks_gallery_1_1'
    ) ) );

    $wp_customize->add_setting( 'blocks_gallery_1_1_title', array(
        'type' => 'theme_mod',
        'default' => 'A selection of our work'
    ));

    $wp_customize->add_control( 'blocks_gallery_1_1_title', array(
        'label' => __( 'Заголовок галереи', 'blockswpdemo' ),
        'type' => 'text',
        'section' => 'blocks_gallery_1_1'
    ));

    $wp_customize->add_setting( 'blocks_gallery_1_1_subtitle', array(
        'type' => 'theme_mod',
        'default' => 'Hand-picked just for you'
    ));

    $wp_customize->add_control( 'blocks_gallery_1_1_subtitle', array(
        'label' => __( 'Подзаголовок ', 'blockswpdemo' ),
        'type' => 'textarea',
        'section' => 'blocks_gallery_1_1'
    ));

Ключевой момент - авторская функция blocks_get_gallery(), которая позволяет получит все параметры и изображений, формирующих галерею.