Trying to display all posts in a category

I don’t know what you tried so far, but below you have a quick answer to list posts from a caategory by its ID.

<?php 
$args = array(
    'posts_per_page'   => -1, // Will show all posts from the category
    'cat'              => 149, // ID of the category
    'orderby'          => 'post_date',
    'order'            => 'DESC',
    'post_type'        => 'post',
    'post_status'      => array('publish')
); 

$posts_list = get_posts( $args );
foreach ( $posts_list as $post ) :
  setup_postdata( $post ); ?> 
    <article>
        <li>
        <?php echo get_the_date(); ?>
        <?php echo get_the_title(); ?>   
        <?php echo get_the_excerpt(); ?>
        Category: <?php echo get_the_term_list( $post->ID, 'category', '', ' ' ); ?>
        </li>
    </article>
<?php
endforeach; 
wp_reset_postdata();
?>